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H^80  .L52  The  origin  and  forma 


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THE  ORIGIN  AND  FORMATION 


DENTAL  FOLLICLE. 


TIIK   FIRST   MEMOIR  ON   THE 


DEVELOPMENT  OF  THE  TEETH. 


DRS.  III.  LKGROS  AND  E.  MAGITOT. 


A   TRANSLATION    FROM    THE    FRENCH,    WITH    INTRO- 
DUCTION  AND   NOTES, 

By  M.  S.  DEAN. 


Authorized  and  REVIEWED  r.v   Dr.  Magitot.  the 
Surviving  Author. 


Including  all  the  Illustrations  of  tue  French  Work,  with  a 
number  op  Additional  Illustrations,  Selected  and  Obiginax 


I'll  [C  LGO: 
JANSKN.    McCLURG    LND  COMPANI 

1880. 


L  SV- 

^ — obu      * 


Copyright,  1879, 
By  M.  S.  DEAN. 


"KNI3HT~t'.~LESNARD       I 


TRANSLATOR'S  PREFACE. 


AN  apology  will  reasonably  be  expected  for  pre- 
-Ol.  seuting  this  translation  to  the  profession. 
It  will  require  but  few  words,  and  I  cheerfully  offer 
it.  The  deficiency  and  inaccuracy  of  the  litera- 
ture, in  our  own  language,  on  the  origin  and  de- 
velopment of  the  "tooth-germ"  and  its  associate 
parts,  render  it  almost  worthless,  as  compared  with 
the  more  recent  researches  of  foreign  investigators. 
The  only  exception  I  would  make  is  that  of  the 
valuable  work  of  Professor  Tomes.  If  anything 
more  is  required,  I  refer  the  reader  to  the  follow- 
ing pages,  which,  so  far  as  I  have  been  able  to  do 
justice  to  the  authors,  will  be  their  own  apology. 

Some  of  you  will  remember  that,  nearly  twenty 
years  ago,  one  of  the  authors  of  this  memoir,  Dr. 
Magitot,  in  connection  with  Dr.  Ch.  Robin,  wrote 
a  treatise  entitled,  The  Genesis  and  Development  of 
the  Dental  Follicle,  to  the  Epoch  of  the  Eruption  of 
the  Teeth,  a  large  portion  of  which  was  translated 
for  the  Dental  ( 'osmos. 

While  the  writers  of  that  treatise  gave  a  detailed 
and  elaborate  account  of  the  development  of  the 
jaws  and  their  anatomical  constituents,  that  por- 
tion devoted  to  the  origin  and  formation  of  the 
dental  follicle  was  in  many  respects  incomplete, 
and  in  some  particulars  erroneous. 


The  improved  methods  of  preparing  sections 
for  microscopic  examination  which  have  since  been 
adopted,  together  with  the  experience  gained  by 
many  years  of  study,  which  one  of  these  authors 
has  since  devoted  to  this  and  kindred  subjects,  has 
enabled  him,  with  the  aid  of  his  eminent  colaborer, 
not  only  to  correct  the  errors  of  that  work,  but 
also  to  describe  these  parts  more  minutely,  and 
with  greater  exactness  than  had  been  hitherto  pos- 
sible. 

While  the  present  work  traverses  a  portion  of 
the  ground  gone  over  by  the  previous  writers,  it  is, 
nevertheless,  a  distinct  memoir,  rendered  more 
comprehensive,  and  more  complete  in  detail,  by 
the  study  of  the  development  of  the  dental  system 
not  only  in  man,  but  in  many  other  mammifera. 

Although  the  work  may  not  be  considered  as  a 
"  practical  treatise,"  in  the  ordinary  acceptation  of 
the  term,  yet  it  contains  valuable  lessons  which 
may  be  applied  in  preventing  the  disastrous  con- 
sequences of  those  exanthematous  diseases  which 
are  so  liable  to  arrest  or  pervert  the  nutritive  sup- 
ply to  these  developing  organs,  and  which  often 
result  in  the  disfigurement,  and  sometimes  in  the 
entire  loss,  of  the  teeth.  Hence  its  suggestions 
should  not  be  confined  to  the  dental  surgeon  alone, 
but  should  be  made  available  by  the  medical  prac- 
titioner, who,  at  the  present  day,  retains  almost 
undisputed  possession  of  this  sadly  neglected  field 
of  practice. 

The  illustrations,  including  copies  of  all  those 
contained  in  the  original,  were  executed  by  Baker 


TRANS!  vrm:  -    PREF  \«  I  .  0 

,i  '  ..  of  thie  city  ;  and.  while  all  of  them,  I  think. 
compare  favorably  with  the  woodcuts  found  in 
similar  works. —  sonic  of  them  showing  the  minute 
detail  of  the  parte  during  the  different  stages  of 
development, —  are  remarkably  faithful  to  nature. 

How  well  the  work  of  the  translator  has  been 
don.-  niusi  be  loft  for  others  to  decide.  It  may  be 
proper  to  state,  however,  that  it  lias  hem  submitted 
to  Dr.  Magitot,  and  meets  with  his  unqualified  ap- 
proval.* 

The  conversational  style  in  which  many  of  the 
notes  have  been  introduced,  may  be  regarded  by 
some  as  unsuited  to  the  character  <>(  a  severely 
scientific  work.  However  this  may  he,  it  certainly 
affords  the  translator  opportunities  of  presenting, 
in  an  easy  and  familiar  manner,  the  views  of  dif- 
ferent authors,  and  some  other  valuable  matter, 
which  he  believes  could  not  otherwise  he  intro- 
duced without  apparent  abruptness.  He  believes, 
also,  that  the  plan  here  adopted  will  relieve  the 
monotonous  strain  upon  the  less  scientific  reader. 
and  that  the  facts  thus  brought  out  will  be  more 
vividly  impressed  upon  most  minds  than  if  pre- 
sented in  the  ordinary  way.  If  this  be  so,  no  other 
defense  is  necessary. 

The  adjectival  terms  denoting  the  species  of 
embryos  —  as  equine,  bovine,  etc..  and  correspond- 
ing to  that  of  human  —  which  have  been  adopted 

*  Extract  from  his  letter.  Paris,  Sept.  8,  L879:  "Jt  trouvt 
eette  traduction  parfaite,  et  je  reconnais  <\>t>   voire  "Trans- 
lator's Introduction'  est  tris  ingenteust    i»>">-  preparer  i< 
r  i'  V intelligence  <lu  mimoin  ." 


6  teanslatoe's  peeface. 

in  the  translation,  I  think,  cannot  be  regarded 
with  disfavor;  the  propriety,  if  not  the  necessity, 
of  their  employment  in  works  of  this  kind  seems 
to  me  unquestionable. 

My  labors  upon  this  work  have  been  light- 
ened by  the  encouraging  words  of  many  leading 
members  of  the  medical,  as  well  as  the  dental,  pro- 
fession; and  to  my  esteemed  friend  and  eminent 
fellow-practitioner,  Dr.  G-.  II.  dishing,  I  am  in- 
debted for  much  kind  assistance  in  preparing  this 
treatise  for  publication.  And  especially  to  Dr. 
Magitot,  the  illustrious  author  of  many  scholarly 
contributions  to  science,  I  must  offer  my  grateful 
acknowledgments  for  the  cheerful  aid  he  has  so 
promptly  rendered  me  in  the  execution  of  this 
work. 

M.  S.  D. 

34  Monroe  Street,  Chicago: 
October,  1879. 


CONTENTS. 


TAOE 

Translators  Introduction,    -  9 

S    I.  Mucous  Membrane,             ...  9 
§  II.  Meckel's  Cartilage  and  Development  of  the 

Jaws,               -  ~" 

§111.  Intermaxillary  Bones,          -            -            -  38 

§  IV.  Definition  of  Terms,       -           -           -  41 

Authors'  Introduction,      -            -            -            -  47 


CHAPTER  I. 

Condition  of  the  Jaws  of  the  Embryo  at  the  period  of 
the  Genesis  of  the  Follicle  — The  Epithelial  Ridge 
(Bourrelet), 48 


ClIAITKi:   II. 

Epithelial  Lamina,  and  the  Genesis  of  the  Enamel- 
organ.  - 


62 


CHAPTER  III. 

Origin  and  Formation  of  the  Dental  Bulb  and  of  the 
Follicular  Wall  (Sac),      -  !,:! 

CHAPTER  IV. 

Phenomena  that  follow  the  Formation  of  the  Follicle 
and  the  Rupture  of  the  Epithelial  Cord,      -  -     115 


8  CONTENTS. 

CHAPTER  V. 

PAGE 

The  Place  and  Mode  of  Origin  of  the  Follicles  of  the 
Permanent  Teeth,  127 

CHAPTER  VI. 

Chronology  of  the  Dental  Follicle,  or  the  Periods  in 
which  its  several  Component  Parts  appear,  -      147 

CHAPTER  VII. 

Criticism  of  Theories,  Resum6,  etc.,  -  -  169 

Conclusions,   ------     181 

Summary  of  Illustrations  and  Brief  Descrip- 
tive Review,     -  -  -  -  -  185 


TRANSLATOR'S  [NTROblJCTION. 


[Teacheb  and  ins  IYiti.s.  Caspbb  ami  Frank.] 

r  I  TEACHER:  I  propose  to  consider  the  Ori- 
-L  gin  and  Formation  of  the  Dental  Follicle 
in  Mammals;  and  for  this  purpose  I  shall  read 
the  valuable  memoir  of  Drs.  Legros  and  Mao-itot, 
which  furnishes  the  most  complete  account  of 
these  phenomena  of  any  work  within  my  knowl- 
edge. I  shall  use  this  treatise  as  a  text,  elabo- 
rating as  .we  proceed,  whenever  suggestions  may 
occur  to  me,  or  in  response  to  questions  from 
you.  In  this  manner  we  may  hope  to  arrive  at 
a  satisfactory  understanding  of  the  subject. 

§  I. -MUCOUS  MK.MBKANE.  ' 

^  on  are  presumed  by  these  authors  to  be 
acquainted  with  the  general  anatomy  ami  physi- 
ology  of   the   parts  from   which    the  teeth   are 


10         translator's  introduction. 

directly  derived.  Indeed,  without  this  knowl- 
edge you  cannot  obtain  a  very  clear  idea  of  the 
origin  and  evolution  of  the  tooth-germs,  even 
from  the  minute  description  given  in  these 
pages.  I  think  it  will  be  well,  therefore,  before 
commencing  our  readings,  to  hastily  reviewT  the 
parts  immediately  concerned  in  the  production 
of  the  teeth,  and  especially  the  epidermis  or 
epithelium,  which  constitutes  the  external  layer 
of  the  mucous  membrane. 

Casper  :  I  ought  to  have  a  pretty  fair  knowl- 
edge of  these  parts ;  if  not,  it  is  no  fault  of 
mine,  for  I  have  faithfully  studied  Biesiadecki, 
Kolliker  and  Klein  ;  and  yet  I  must  confess  that 
my  knowledge  is  badly  confused,  especially  in 
regard  to  the  mucous  membrane;  for  these 
authors  do  not  represent  this  tissue  by  descrip- 
tive figures,  as  they  do  the  skin.  Besides,  the 
names  given  to  the  different  strata  are  a  good 
deal  mixed ;  so  that  I  think  a  review  of  the 
subject  will  not  be  a  waste  of  time. 

Teacher:  The  difficulties  you  have  encoun- 
tered do  not  surprise  me ;  for  I  have  myself  had 
considerable  trouble  in  determining  even  the 
location  of  the  layer  which  some  authors  have 
described  under  that  name.     For  example : 


MUCOUS    WEMBBANE.  11 

I  I  i  A.ecording  to  Borne  authors,  the  epidermis 
alone  constitutes  the  mncous  membrane  (Guillol 

and  others).* 

(2)  According  to  others,  the  mucous  mem- 
brane consists  of  three  membranes,  viz.,  "an  epi- 
thelium, a  proper  mucous,  and  a  fibrous  coat." 
"The  second  coat,  the  proper  mucous  membrane, 
is  apparently  without  texture.  The  third  coat 
corresponds  to  the  corium  of  the  skin.'' 

This  is  Prof.  Hand's  definition  of  the  mucous 
membrane,  and  essentially  that  of  Prof.  Leidy. 
Here  we  have  the  term  mucous  membrane  used 
both  in  a  general  and  a  special  sense,  as  a  whole 
and  as  an  integral  part;  the  mucous  membrane 
consisting  of  three  layer*,  one  of  which  is  the 
proper  mucous  membrane,  and  the  latter  seem.-. 
from  its  description,  to  be  identical  with  the 
''basement  membrane"  of  Todd  and  Bowman, 

*Prof.  Wedl,  in  his  "Pathologie  der  Z&hne"  (Leipzig, 
1870),  under  the  heading  of  Development  of  the  Teeth, 
designates  the  mucous  membrane  as  an  epithelial  structure, 
and  calls  the  enamel-organ  a  follicle  of  mucous  cells: 
"Dieser  Schleimzellenschlauch  wurde  von  Ko'lliker  als 
Schmelzkeim  bezeichnet."  This  phraseology,  to  one  who 
had  studied  Frey,  Magitot,  Kolliker,  Flint,  Klein,  and 
many  other  physiologists  who  have  described  the  mucous 
membrane,  would  render  Wedl's  description  unintelligible. 


12         translator's  introduction. 

the  "intermediate  membrane"  of  Henle,  and  the 
"membrana  propria"  of  Kolliker  and  others. 

(3)  According  to  others,  again,  the  layer  situ- 
ated immediately  heneath  the  stratum  Jfalpighii 
(and  which  corresponds  with  the  corium  or 
dermis  of  the  skin)  is  "the  proper  mucous 
membrane"  (Kolliker,  Klein,  Flint,  Frey  and 
others).  These  authors,  however,  designate  the 
lower  portion  of  .the  epidermis  of  the  skin  by 
an  equivalent  term,  mucous  layer  j  but  occasion- 
ally they  use  the  expression  mucous  membrane 
in  its  general  sense. 

(4)  Again,    Dunglison    and    many   other   au- 
thors  employ    the   term   mucous   membrane   in« 
its  broader  sense,  as  including  the  "epidermis" 
and  the  subjacent  layers.* 

You  see,  therefore,  that  the  study  of  this 
membrane  is  rendered  unnecessarily  difficult  by 
the  numerous  and  often  contradictory  terms 
which  different  writers  use  in  describing  it. 

*  Dunglison  says:  "In  the  mucous  membrane  the  same 
superposition  of  strata  is  generally  considered  to  exist  as 
in  the  skin,  viz.,  epidermis  or  epithelium,  rete  mucosum, 
corpus  papillare,  and  cutis  vera." 

M.  Flourens  divides  all  the  mucous  membranes  into 
three  layers — the  derma,  epidermis  and  corpus  mucosum. 


Ml  COUS    MEMBRANE. 


13 


Kolliker  and  those  of  his  Bchool  divide  the 
mucous  membrane  (as  a  whole)  into  the  follow- 
ing layers,  counting  from  the  external: 

ill  Ejntheli/um;  (2)  mevthnmii  mucosa  (the 
proper  mucous  membrane);  (3)  submucosa  (sub- 
mucous membrane i,  tela  rmtcosa,  etc. 


Fig.  1. 

1st  Class.   2d  Class.   3d  Class.  4th  Class. 


= 


|      Strat.  corn. 

s 

- 

a 

-     Strat.  Malp. 

If.  memb. 

o 

■ 

Basement  niemb. 

M.  memb. 

t-        .    \  Par*  pap. 
Dermis-  _ 

(  Par-  ret. 

M.  memb. 

3 

CD 
= 

Snbdermls. 

- 

Fig.  1. — The  above  diagram  shows  the  relative  position 
of  the  different  layers  which  are  designated  the  mucous,  or 
"'proper"  mucous  membrane  by  various  writers.  The 
column  on  the  left  gives  the  names,  and  location  of  the 
strata  of  the  mucous  membrane  as  we  think  they  should 
be  designated.  The  horizontal  lines  show  the  relative  loca- 
tion of  these  layers,  without  any  regard  to  their  thickness. 

Some  of  these  authors  call  the  external  por- 
tion of  the  "membrana  mucosa"  the  chorion, 
corinm  or  derma.  .They  also  divide  the  "proper 
mucous  membrane'9  into  two  layers,  the  pajril- 
hinj  and  the  reticulary. 

Huxley     says     the    skin    and     mucous     mem- 


■14 

brane  "may  be  distinguished  into  three  por- 
tions; a  central  plane  of  indifferent  tissue  [the 
basement  membrane],  from  which,  growth  and 
metamorphosis  take  place  externally,  to  consti- 
tute the  representative  of  epidermis  or  epithe- 
lium, to  which  we  propose  to  give  the  name  of 
ecderon  /  while  internally,  growth  and  meta- 
morphosis take  place  from  the  central  plane,  so 
as  to  constitute  the  representative  of  the  derm 
or  'mucosa,'  which  we  have  termed  the  en- 
deron."* 

ISTow,  since  the  terms  emploj^ed  by  different 
writers  to  designate  the  layers  of  the  skin  and 
of  the  mucous  membrane  are  so  various,  and 
sometimes  conflicting,  I  shall  apply  the  same 
terms  to  the  corresponding  strata  in  both  of 
them,  as  follows : 

(1)  The  term  epidermis  will  comprehend  the 
whole  of  the  external  epithelial  layer,  whether 
it  be  of  the  skin  or  of  the  mucous  membranes. 
(2)  The  term  dermis  will  be  applied  to  the 
stratum  immediately  subjacent  to  the  epidermis, 
and  which  is  known  by  the  various  terms,  cu- 
tis vera,  corium,  mucosa,  proper  mucous  mem- 

*Appendix  to  the  Sydenham  edition  (4th  edition)  of 
Kolliker's  Histology. 


MUCOUS    MEMBRANE.  15 

brane,  etc.  These  two  layers  will  be  subdi- 
vided,—  the  epidermis  into  two  strata  —  the 
corneous  and  Malpighian ;*  the  dermis  also 
into  two  parts,  the  papillary  and  retioulary. 

The  tissues  next  subjacent  to  the  dermis 
will  he  known  as  the  subdermis,  corresponding 

to  the  subcutanea,  subniucosa,  tela  mucosa,  etc. 

In  thus  applying  these  terms  I  make  no  new 
departure  in  our  nomenclature,  but  merely  cm- 
ploy  the  old  ones  more  systematically,  and,  I 
think,  more  rationally. 

It  must  be  confusing  to  the  student  to  find 
the  lower  layer  of  the  epidermis  of  the  skin, 
and  the  layer  that  lies  beneath  the  epidermis  of 

*The  Malpighian  layer,  as  defined  by  most  authors, 
includes  those  epithelial  cells  (of  the  epidermis)  that  lie 
subjacent  to  the  horny  layer,  whether  their  form  be  colum- 
nar, polygonal  or  otherwise;  but  some  authorities,  among 
whom  are  Legros.  Magitot,  Tomes  and  Ki'iss.  limit  the 
term  stratum  Malpighii  to  the  lowest  layer  of  cells,  which 
stand  vertically,  like  palisades,  upon  the  surface  of  the 
dermis.  This  single  layer  of  columnar,  or  cylindrical  cells, 
as  they  are  sometimes  called,  is  also  termed  the  prismatic 
layer  by  Legros  and  Magitot, —  a  term  which  is.  to-my  mind, 
definite  and  not  liable  to  mislead  the  student ;  and  hence 
will  be  employed  in  the  following  translation  wherever  it 
occurs  in  the  original. 


16         translator's  introduction. 

the  mucous  membrane, —  parts  which  are  locally, 
anatomically,  and  functionally,  different, —  both 
designated  by  the  same  name;  and  not  to  find 
a  dermis  beneath  the  epidermis.  The  term  der- 
mis cannot  be  objected  to,  as  applied  to  a  layer 
of  the  mucous  m.embrane,  since  the  growths 
originating  in  this  stratum  are  universally  de- 
nominated dermhl  tissues. 

For  the  reasons  here  stated,  I  believe  I  am 
justified  in  adopting  the  simple  S}7stem  of  ter- 
minology indicated  above. 

With  this  designation  of  terms,  we  will  pro- 
ceed with  our  description  of  the  mucous  mem- 
brane, and  more  especially  the  exterior  layer  — 
the  epidermis,  from  which  the  tooth-germs 
directly  originate. 

The  mucous  membrane  and  the  shin  are  an- 
atomically analogous  and  continuous  structures. 
The  first  clothes  the  internal,  and  the  other  the 
external,  surfaces ;  and  the  description  of  the 
one  will,  with  slight  modifications,  apply  to  the 
other.  In  a  general  sense,  they  are  composed 
of  two  strata  or  layers,  the  dermis  and  the  epi- 
dermis}  yet  for  convenience  of  description, 
rather  than  for  any  other  reason,  they  have 
been  variously  subdivided. 


.Ml  <  OUfl    MEMBRANE.  17 

The  externa]  stratum,  the  epidermis,  com- 
posed entirely  of  epithelial  cells,  lias  be(Sn  de- 
Bcribed  as  consisting  of  two  layers  — the  exter- 
nal being  termed  the  corneous  and  the  internal 
the  MaVpighian.  The  "scarf-skin"  raised  on  the 
external  surface  of  the  skin  by  a  blister,  and 
the  pellicle  detached  from  the  palate  by  hot 
drinks,  represent  the  corneous  layer  of  the  epi- 
dermis ;  by  some  authors  this  is  called  the 
"true  epidermis,"  and  by  some  the  "cuticle.'1 
This  layer  is  composed  of  the  old  epithelial 
cells  which  have  ceased  to  perform  any  of  the 
vital  functions.  The  subjacent  layer,  formed  of 
living  epithelial  cells,  which  vary  in  form  and 
size,  is  denominated  (among-  many  other  terms) 
the  stratum  Maljrighii. 

Underneath  these  two  subdivisions  of  the  epi- 
dermis of  the  mucous  membrane  (according  to 
the  nomenclature  here  adopted)  we  shall  find 
the  dermis  {derm  or  derma).  .But  lest  I  should 
mislead  you  I  will  mention  here  that  there  is  a 
transparent  amorphous  pellicle  which  separates 
the  lower  stratum  of  the  epidermal  cells  from 
this  latter  layer.  This  structureless  tissue  is 
described  by  Todd  and  Bowman  under  the  name 
of  basement  membrane,  and  by  Eenle  under  that 


18         teanslatoe's  introduction. 

of  intermediate  membrane.  Now,  although  the 
existence  of  a  "membrane"  here  is  disputed  by 
many,  yet  there  can  be  no  doubt  that  a  homo- 
geneous structure  is  interposed  between  these 
layers,  and  that  in  some  parts  it  presents  the 
character  of  a  membrane  of  considerable  thick- 
ness. This  membrane  is  of  peculiar  interest  to 
the  dental  physiologist,  since  the  dentine-bulb 
and  the  enamel-organ  will  be  found  on  the 
opposite  sides  of  it.  In  this  situation  it  consti- 
tutes the  membrana  jprmformativa  of  Raschkow. 
This  tissue  is  not  usually  reckoned  among  the 
layers  of  the  skin  and  mucous  membrane;  and 
its  further  discussion  here,  as  a  preformative 
membrane,  would  be  but  to  anticipate  what  will 
follow  in  the  body  of  this  work. 

Inasmuch  as  the  elements  of  the  epidermal 
membrane  (the  epithelium)  play  the  most  im- 
portant part  in  the  development  of  the  teeth, 
as  will  be  seen,  hereafter,  a  more  minute  de- 
scription will  be  given  of  them  than  of  those 
of  the  subjacent  stratum. 

These  elements  are  derived  from  the  exter- 
nal germinal  layer  —  the  corneous  leaf  or  plate, 
(Remak),  or  the  epiblast,  as  it  is  now  more  gen- 
erally called.     They  are  developed  at  an  earlier 


MUCOUS     MEMBRANE.  19 

period  in  embryonal  life  than  are  the  connect- 
ive-tissue cells  of  the  middle  or  intermediate 
layer  —  the  mesoblast,  from  which  the  dermis 
originates. 

As  early  as  the  35th  day  (as  nearly  as  I  am 
able  to  ascertain)  the  epidermis  presents-  two 
layers  of  cells ;  but  at  this  period  it  cannot  be 
regarded  as  a  membrane  composed  of  two  1am- 
in;v,  for  the  external  cells  haye  not  yet  attained 
the  requisite  age  to  mature  them  into  the  horny 
bodies  that  constitute  the  corneous  layer.  The 
cells  constituting  the  epidermis  must,  therefore, 
though  differing  in  form,  be  regarded,  at  this 
stage,  as  belonging  exclusively  to  the  Malpigh- 
ian  stratum  (in  its  broader  sense).  But  soon  the 
transforming  hand  of  time  will  convert  them 
into  the  corneous  layer ;  when  the  oral  epider- 
mis will  be,  like  that  of  the  skin,  divisible  into 
two    laminae.*     If  we  examine    these    two  epi- 

*  In  his  last  edition  (5th),  under  the  head  of  "Epithe- 
lium of  the  cavity  of  the  mouth,'"  Kolliker  remarks  that 
"the  elements  that  constitute  this  epithelium  [epidermis] 
are  not  divisible,  like  the  epidermis  [of  the  skin],  into  two 
clearly  distinct  lamina?,  but  constitute  one  connected  layer, 
more  resembling  the  mucous  layer,  but  representing  also 
^the  corneous  layer." 

It    may  In'  true    that  in  some  portions   this   epidermis 


20         translator's  introduction. 

dermal  strata  of  the  mucous  membrane  more 
closely,  we  shall  find  them  composed  of  quite 
regular  layers  of  epithelial  cells,  which  (com- 
mencing with  the  lowest)  may  be  described  as 
the  infant  cells,  the  youthful  cells,  the  adult 
cells,  the  aged  cells,  and  the  dead  cells. 

The  cells  composing  the  stratum  corneum 
belonged  in  their  infancy  to  the  lowest  layer 
of  the  stratum  Malpighii ;  in 
their  youth  to  a  more  external 
layer  known  as  the  "  prickle," 
"spinous,"  "ridged,"  "acu- 
leated,"  or  "imbricated"  cells 

(all  of  which  terms  are  applied 

,,  ,     .       _.        Fig.  2. — "Spinous," 

to  cells   represented    m    Fig.    «ridged,"or"imbri- 

2).  In  their  middle  life  they  cated"  cells.  (From 
belonged  to  the  polygonal  r 
cells  ("pavement,  or  tessellated  epithelium"), 
which  lie  still  nearer  the  surface ;  and  in  their 
old  age,  to  the  elongated,  flattened  cells,  in  which 
the  nuclei  have  nearly  disappeared  :  and  finally, 

is  not  so  readily  divisible  as  that  of  the  skin  ;  but  it  is 
known  with  what  facility  a  pellicle  may  be  raised  from 
the  palatal  portion  —  the  rugae  for  example  —  by  drinks 
that  are  not  sufficiently  hot  to  produce  the  same  effect 
upon  the  skin. 


MUCOUS    MEMBRANE.  21 

as  dead  cells,  they  occupy  the  most  outward,  the 

corneous  layer  of  the  epidermis. 

The  cells  of  the  lowest  layer  (the  infant  cells) 
stand    vertically,  like    palisades,  upon  the  base 
merit  membrane  (c);   which  latter  separates  the 
epidermal    from    the  dermal 
Btratum  of  the  mucous  mem- 
brane;   or  in    other    words, 
the      basement       membrane 
separates  the  epithelium  from 

the  "  mucosa,"  "  proper  mi.-       FlG-3-~«.  cylinder, 

columnar  or  prismatic 
cous  membrane,"   or    "  cori-  cells   of    the    mucous 

urn."       These    cells,    which   membrade,  or  "infant 

cells";  fr,  intermediate 

may  lie  likened  to  the  blocks  matterj     c,    basement 

of    a     Nicholson     pavement   membrane;    d,   fibrous 

,  ,    .  .  .  .     tissue    of   the   dermis. 

when  set  in  position,  consti-  {FromFrejfm  Diagram- 

tute  what  is  called  variously  matic.) 
the  prismatic,  columnar,  cylindrical,  and,  per- 
haps less  properly,  the  Malpighian  layer.  They 
have  large  oval  nuclei,  and  are  said  to  be  desti- 
tute of  a  cell-wall.  In  the  embryo  (according  to 
Ilenle)  they  appear  like  a  stratum  of  protoplasm 
regularly  studded  with  nuclei.  This  layer  of 
prismatic  cells  offers  additional  interest  to  the 
dental  student,  since  it  constitutes  the  peripheral 
portion  of  the  enamel-organ,  including  that  spe- 


22  TRANSLATORS    INTRODUCTION. 

cial  area  which,  during  the  course  of  develop- 
ment, will  be  known  as  the  "enamel-membrane" 
("  internal  epithelium  of  the  enamel-organ  "  of 
Kolliker,  or  "membrana  adamantina'''  of  Rasch- 
kow),  and  which  here  either  is  converted  into 
enamel  or  produces  it.  But  more  of  this  anon. 
The  next  layer  or  layers  of  cells  (the  youthful) 
have  grown  larger,  and,  besides  their  imbricated 
appearance,  are  surrounded  by  a  thin  cell-wall, 
periplast  (Huxley),  or  formed  material  (Beale). 
The  cells  external  to  these  assume  larger  propor- 
tions and  are  more  polygonal  in  form,  and  repre- 
sent these  cells  in  their  middle  life.  The  cell- 
wall,  or  periplast,  has  increased  in  thickness,  while 
the  nucleus  has  proportionally  diminished  in  size. 


Fig.  4.  Fig.  4. —  This   cut    was 

designed  to  illustrate  the 
cells  of  the  epidermis.  E, 
in  some  of  their  various 
phases,  as  described  above. 
E-{  yjpSg1     zL^_^^    jig  a,    Stratum    corneum;    b, 


stratum  Malpighii,  with 
its  prismatic  or  columnar 
layer  resting  upon  the 
basement  membrane  b  m; 
c,  the  upper  portion  of 
the  dermis.  The  papillse 
are  not  represented  in  this 
figure,  nor  is  the  subdermal  layer. 


MT«  0U8    MKMI'.KANK. 

The  cells    still    external  to   these  are  I 

aid  the  nearer  they  approach  the  corneous 
stratnni  the  larger  will  be  '  the  amount  of 
"formed  material"  that  surrounds  the  nucleus; 
till  at  last  only  a  trace  of  the  latter  is  visible, 
or  it  entirely  disappears,  and  these  cells  enter 
the  horny  layer    and  become  the  Us — 

a  lifeless  protecting  covering  for  the  living  ce- 
ments that  are  growing  up  beneath. 

Thus  these  cells,  during  their  passage  from 
the  interned  to  t?t<:  external  surface,  have  un- 
dergone all  these  changes,  until  from  prismatic 
or  columnar  cells  they  have  finally  become  thin, 
98  scaleSi  which  are  continually  cast  off"  as 
foreign  or  etfete  matter.  During  the  entire  life 
oi'  a  person  these  cells  are  continually  passing 
away  ;  and  hence  the  production  oi  new  genera- 
tions of  them  must  be  equally  incessant.  This 
reproduction  takes  place  from  the  lower 
oi  vertical  cells,  i.  «.,  the  cells  that  constitute 
the  prismatic  or  columnar  layer:  at  least  this 
is  now  the  most  generally  accepted  opinion  of 
physiologists,  though  with  some  respectable  ex- 
ceptions. 

The  external  layer  (stratum  oom&um)  of  the 
mucous  membrane,  unlike  that  of  the  skin,   is 


24         translator's  introduction. 

permeable  by  various  kinds  of  liquids;  which, 
after  passing  through  the  softer  portions  of  the 
epidermis  and  the  basement  membrane,  may  be 
absorbed  by  the  vessels  of  the  dermis  (proper 
mucous  membrane,  corium).* 

tTow,  lest  your  patience  be  too  heavily  taxed, 
we  will  take  only  a  very  hasty  glance  at  the  sub- 
jacent layer  of  the  mucous  membrane,  ignoring, 
for  the  time  being,  the  existence  of  the  basement 
membrane. 

Lying  immediately  beneath  the  epidermis  we 
find  a  fibro-vascular  membrane  of  variable  thick- 
ness, which  we  call  the  dermis  (the  proper 
mucous  membrane,   the  mucosa,   mucous  layer, 

*  Kolliker  (Loc.  Cit.,  5th  ed.j  says:  "  The  epithelium  of 
the  mouth,  though  thick,  is  very  pervious,  a  characteristic 
which  distinguishes  it  from  the  epidermis  [of  the  skin],  of 
which  the  mucous  layer  [stratum  Malpighii]  alone  possesses 
this  quality.  It  allows  the  various  kinds  of  liquids  to  pass 
through  it  from  without  inward,  which,  when  brought  in 
contact  with  the  mucous  membrane  [the  dermis],  may  be 
absorbed  by  the  vessels,  or  become  cognizant  to  the  nerves 
received  by  this  membrane." 

Kolliker  does  not  recognize  the  existence  of  nerves  in 
any  part  of  the  epidermis.  If  the  experiments  of  Langer- 
ghans  and  Podcopaew  are  reliable,  the  liquids  need  only 
enter  the  Malpighian  layer  to  be  brought  in  contact  with 
the  nerve  filaments  that  penetrate  this  soft  layer. 


Ml  PODS    MEMBRANE.  L<;, 

cutis  vera,  corinm,  chorion,  etc.)     Thia  is  con- 
tinuoua  with  the  dermis  of  the  skin,  and  gradu- 
ally  merges  into  the  subdermal  areolar  tissue, 
with   whirl,   it   is  strongly  and   intimately  con' 
nected.     The  externa]   portion  of  the  dermis 
known  as  the  pars  papillaris  (papillary  part), 
;""1  the  subjacent  portion  as  thenars  reticularis 
reticulary  or  netted  part).     But  we  cannot  dwell 
upon  these  particulars,  which  do  not,  in  fact,  exist 
in   the  dermis  at  the  early  period  of  embryonal 
life    when    the   development  of  the   teeth   com- 
mences.     J   will    .ay,   however,   that   the   promi- 
nent constituents  of  the  dermis  are  the  connective 
tissue  elements;  hut,  as  before  stated,  the  cells 
of  the  mesoblast,  to  which  this  layer  belongs,  are 
no!    developed   at  so  early  a  period   as  those  of 
the  epibUst,  from  which  the  epidermis  is  derived. 
For  example,  till  the  forty-fifth  day  of  gestation^ 
••""1  perhaps  later,  the  'dermis  is  represented  by 
a  nucleated  mass  of  embryonal  tissue,  in  progress 
of  evolution,  while  at  the  same  stage  the  epi- 
dermal cells  are  completely  developed. 

From  tfu  external  surface  of  t7u  dermis  rises 
the  dentine^ulb,  or  dentinal  papilla;  though 
many  authors  Mate  that  the  papilla  originates  in 

the   "submucous"   tissue.      This    latter   tissue   or 


26         translator's  introduction. 


membrane  corresponds  with  what  I  have  termed 
the  subdermal  tissue.     But  to  me  it  is  evident 
that  the  dentinal  papilla  first  appears  as  a  little- 
nodule  upon  the  surface  of  the  layer  subjacent  ' 
to  the  basement  membrane  —  the  dermis. 


Fig.  5. 


Fig.  5.— This  cut 
is  taken  from  Bolli- 
ker's  Man'l  of  Hist. 
It  has  been  widely 
copied  by  histologi- 
cal writers,  and  rep- 
resents   "a    simple 
papilla  [of  the  mu- 
cous       membrane], 
with  manifold  ves- 
sels and  epithelium, 
from  the    gums  of 
an  infant,  magnified 
250  diam."      It  is 
given    here    princi- 
pally to    show   the 
epidermal  covering,, 
though  the  cells  are 
represented  only  approximately  correct,  the  figure  being  de- 
signed mainly  to  illustrate  the  vessels  of  the  papilla.   It  will 
be  observed  that  the  "ridged"  cells  do  not  appear  m  this. 

With  this  imperfect  description,  which  has 
been  confined  mostly  to  the  situation  of  the  lay- 
ers, and  to  some  of  the  more  conspicuous  elements 
of  the  mucous  membrane,  I  must  drop  this  fasci- 
nating subject ;  hoping,  however,  that  what  has 


I'l  \  BLOPMBNT   OF   THE    3  a  \\  8, 


a  i 


been  said  will  repay  the  time  it  has  occupied, 
and  more  especially  thai  the  little  information 
you  have  thus  gained  will  stimulate  you  to  seek 
a  more  thorough  knowledge  of  thi.s  very  impor- 
tant, and  very  extensive,  branch  of  histology  and 
physiology. 

§  tt.— THE  EARL1    DEVELOPMENT  OF  THE  JAWS; 
AND  MECKEL'S  CARTILAGE^ 

As  Meckel's  cartilage  is  alluded  to  in  the  first 
pages  of  the  following  treatise,  perhaps  1  had 
better  anticipate  your  questions  in  regard  to  it; 
for  a  description,  that  would  be  at  all  satisfactory, 
would  make  too  long  a  break  in  the  text. 

1'  bane  :  I  have  seen  this  cartilage  mentioned 
in  various  works,  but  never  described;  and  I  am 
curious  to  learn  something  of  this,  to  me,  myste- 
rious organ. 

Ceaohee:  Since  our  medical  and  dental  liter- 
ature is  so  reticent  in  regard  to  this  important 
embryonal  structure,  and  the  authors  of  this 
work  scarcely  more  than  allude  to  it.  I  will  give 
you  a  very  brief  historical  account  of  it.  The 
facts  that  1  Bhall  give  you  regarding  it  have  been 
gathered  mainly  from  a  treatise  written  b\  Drs. 
M.'igitot  and  Rubin  (the  first   named  being  one 


28         translator's  introduction.  . 

of  the  authors  of  the  present  work),  in  which  this 
subject  is  very  fully  elaborated,  and  from  which 
most  of  the  illustrations  here  given  are  copied. 

I  will  commence  at  a  period  some  ten  days 
anterior  to  the  origin  of  the  cartilage,  and  briefly 
sketch  the  progressive  development  of  the 
jaws  till  it  makes  it  appearance ;  and  then  trace 
their  phenomena  together  to  the  time  when  it 
disappears. 

If  we  examine  a  human  embryo  of  fifteen  to 
eighteen  da}rs  (total  length,  little  over  half  an 
inch),  we  shall  find  two  tubercles  which  proceed 
from  the  first  visceral  arch,  and  which,  when  de- 
veloped, will  constitute  the  lower  jaw.  These 
tubercles,  processes,  tongues,  apophyses  or  bour- 
geons (take  your  choice  of  these  terms)  gradually 
approach  each  other  until  they  unite  at  the  me- 
dian line,  and,  at  a  later  period,  become  ossified. 

This  union  takes  place  about  the  twenty-eighth 
day,  at  which  period  the  embryo  has  attained 
perhaps  three-fourths  of  an  inch  in  length.  But 
coincidently  with  the  growth  of  these  two  pro- 
cesses, two  other  bourgeons,  or  buds,  shoot  out 
from  the  same  "  visceral  arch  "  to  form  the  supe- 
rior maxilla.  (Fig.  6,  5,  5).  (Fig.  7,  g,  g). 
•  The   growth    of    these   is   also    toward    each 


DEVELOPMENT   OF   THE   JAWS 


29 


otlu-r;  bat,  unlike  the  former  two,  they  never 
UUiU'  with  each  other  aor  meet  at  the  median 
line:  for  there  is  still  a  third  pair  of  bourgeons, 
called  the  incisive  or  intermaxillary,  which 
arise  from  the  forehead  or  frontal  apophysis; 
and  these,  in  their  downward  growth,  occupy 
the  central  portion  of  the  open  space  between 
the  maxillary  processes.  This  will  be  seen  by 
a  -lance  at  Fig.  6,  4,  and  Fig.  7,  II,  although 


Kig.  G. 


L^ 


Fig.  6.— Mouth  of  an 
embryo     of    forty    days. 
(Coste.)     1,  First  appear- 
ance of  the  nose.     2.  2, 
First  appearance  of  the 
abe  of  the  nose.    3,  Ap- 
pearance of  the  closure  be- 
neath the  nose.   4,  Middle 
or  median  portion  of  the 
upper  lip  forme,/   lnj  the 
approach  and  union  of  the 
two    incisive    proa  ust  s  ■ 
the   little    notch    in    the 
median  line  still  indicat- 
ing the  primitive  separa- 
tion of  the  two  processes. 
5,  •").    Superior   maxillary 
processes     forming     the 
lateral  portion  of  the  up- 
per lip.    6,  6,  Groove  for 
tli''   development  of   the 


lachrymal  sacs.  7,  Lower  lip.  8,  Mouth.  9, 9,  Lateral  halves 

of  the  palatini  arch,  already  nearly  approximate!  in  front 
but  still  widely  separated  behind. 


30 


TRANSLATORS    INTRODUCTION. 


they  have,  in  these  cuts,  already  united  with  each 
other  at  the  median  line.  These  last-named  pro- 
cesses, when  ossified,  will  constitute  the  inter- 
maxillary bones.  A  line,  faintly  representing 
the  point  of  union  of  these  two  processes,  may 
be  seen  in  Fig.  7,  but  is  not  portrayed  in  the 

Fig.  7. 


Fig.  7. — A  vertical  section  of  the  anterior  part  of  the 
face  of  a  human  embryo  of  forty  to  forty-five  days.  Magni- 
fied 80  diameters.  (Magitot.)  a,  a,  Meckel's  cartilage; 
F,  F,  F,  F,  the  mouth;  g,  g,  superior  maxilla?;  H,  H, 
incisive,  or  intermaxillary  processes;  the  perpendicular 
line  showing  their  point  of  union  with  each  other. 


DEVELOPMENT    OF   THE   JAW8.  3] 

original  plate.  It  is  added  here  to  avoid  givine 
yon  the  impressioD  that  this  iQ&aingle  process. 
There  is  a  slight  notch  or  clefi  still  remaining  at 
the  lower  margin,  between  the  intermaxillary 
processes  (Fig.  63  4),  which  in  a  subject  a  few 
•  lavs  older  would  have  been  closed. 

Soon  after  the  intermaxillary  processes  have 
become  united  with  each  other  (say  in  rive  to 
eight  days),  their  free  lateral  margins  form  a  junc- 
ture, and  coalesce  with  the  advancing  superior 
maxillary  processes,  thus  closing  the  vertical  clefts 
seen  in  Fig.  7  (above  the  letters  F),  with  the  ex- 
ception of  two  small  apertures  for  the  nostrils. 
(Fig.  6,  2,  2.)  All  these  processes  are  outgrowths 
from  the  mesoblastic  layer,  clothed  externally 
with  a  coat  of  epithelium  from  the  epiblastic. 

From  this  brief  sketch  of  the  mode  of  devel- 
opment of  the  maxillary  and  intermaxillary  pro- 
cesses you-  will  readily  comprehend  the  origin 
of  that  common  malformation  known  as  hare- 
lip. When  from  any  cause  one  of  the  maxillary 
bourgeons  fails  to  unite  with  the  intermaxillary 
process,  we  have  "simple  hare-lip";  a  similar 
failure  on  both  sides  results  in  "double  hare-lip." 
If.  in  addition  to  these  lateral  fissures,  one  occurs 
at  the  median  line  (which   is  not  frequent),  we 


32  translator's  INTRODUCTION". 

have  "complicated  hare-lip."  Occasionally  there 
is  the  central  fissure  alone,  in  which  case  the 
intermaxillary  processes  have  failed  to  coalesce 
with  each  other  —  a  rare  occurrence. 

"We  Avill  now  return  to  the  lower  jaw.  As 
before  stated,  the  processes  (sometimes  called  the 
mandibular),  from  which  this  maxilla  is  devel- 
oped, meet,  from  about  the  twenty-fifth  to  the 
twenty-eighth  day,  and  form  a  union  with  each 
other  at  the  median  line.  (Fig.  6,  7.)  Very  soon 
afterward  a  little  cartilaginous  band  makes  its- 
appearance  ("  by  direct  genesis "),  and  occupies 
the  central  portion  of  the  embryonal  mass  that 
now  represents  the  lower  jaw.     This  is 

Meckel's  cartilage 

in  its  incipient  stage  of  development.  It  is  a 
small  whitish  cord,  lying  in  a  bed  of  soft  trans- 
parent tissue,  and  may  be  easily  distinguished  by 
the  aid  of  a  low  magnifying  power;  and  by  care- 
ful manipulation  it  may  be  removed  entire  from 
the  surrounding  mass  for  examination.  This  car- 
tilage was  first  noticed  and  described  (in  1820,  I 
think,)  by  the  celebrated  German  anatomist  whose- 
name  it  bears.  It  gives  form  and  stability  to  the 
lower  jaw  of  the  embryo,  serving  as  a  temporary 


MECKEL  -    I  AIM  ll  \(.l.. 


33 


skeleton,  from  an  early  period  till  it  is  no  longer 

iifi'tlcd  i'(.r  that  purpose.  It  is  composed  of  two 
symmetrica]  or  homologous  parte  (corresponding 
to  the  right  and  left  sides  of  the  jaw),  which 
soon  become  united  at  the  ?//<  nf<il  symphysis. 
From  this  point  <>t'  juncture  they  extend,  one  <>n 
either  side,  to  the  frame  of  the  tympanum,  where 
they  terminate  in  the  malleus.     |  Pig.  s.  b.) 

Fig.  8.  Fig.  8.— Cranium 

of  a  human  foetus  of 
four  months,  natural 
size.  Dissected  for 
the  purpose  of  show- 
ing the  membrane 
of  the  tympanum  at 
this  age,  with  the 
cartilages  of  the  in- 
cus and  of  the  mal- 
leus (b);  also,  the 
extra-tympanic  por- 
tion of  Meckel's  car- 
tilage [a  i.  [Magitot 
(nid  Rubin). 

This  cartilage  is  said  to  constitute  the  first 
solid  structure  that  appears  in  this  visceral  arch  ; 
and  from  its  commencement  (about  the  twenty- 
fifth  day),  until  it  entirely  disappears,*  it  under- 
goes a  constant  series  of  modifications. 

*  Although  Meckel.  Valentin,  and  sonic  others,  extend 
the  existence  of  this  cartilage  to  the  eighth  month  in  the 


34         translator's  introduction. 

It  has  scarcely  attained  its  full  growth  (which 
period  corresponds  to  the  commencement  of  the 
ossification  of  the  malleus),*  when  it  begins  to 
waste  away  and  disappear. 

Between  the  thirty-fifth  and  the  fortieth  days 
of  embryonal  life,  slight  traces  of  ossification  show 
themselves  at  points  nearly  equidistant  between 
the  symphysis  and  the  angle  of  the  future  jaw. 
This  extends  rapidly,  both  anteriorly  and  pos- 
teriorly, along  the  external  face  of  Meckel's  carti- 
lage, in  immediate  contact  but  not  uniting  with 
it ;  and  at  about  the  sixtieth  day  of  gestation  a 
miniature  jaw-bone  is  formed,  though  not  yet 
perfected.     (See  figure  below.) 

»    Pig.  9.  Yig.  9. — Taken  from  a  human  embryo  of 

^JSSgZ^g  about  sixty  days.  Natural  size.  Soft  parts 
"  removed,  showing  Meckel's  cartilage  and  the 

inner,  or  lingual  face  of  the  jaw-bone,  left  side.  The  cartilage 
has  much  the  appearance  of  a  very  large  hog-bristle.  The 
main  object  in  presenting  this  figure  is  to  show  the  stage  of 
development  at  this  early  period,  i,  Symphysis;  a,  extra- 
tympanic  portion  of  Meckel's  cartilage;  n,  manubrium  mal- 
lei.    (Original  figure.) 

human  foetus,  yet  Drs.  Magitot  and  Eobin  state  that  they 
have  never  been  able  to  find  a  trace  of  it  later  than  the  sixth 
month.  As  for  myself,  I  have  never  succeeded  in  finding  the 
slightest  vestige  of  it,  even  at  the  symphysis,  at  the  end  of 
the  fifth  month. 

*  The  latter  part  of  the  third  month  of  embryonal  life. 


MKCkhl.  S     ('AIM  II.  \i;| .. 


35 


At  tin's  epoch  the  skeleton  of  the  lower  jaw 
is  composed  of  tw<>  arches  (if  we  may  include 
Meckel's  cartilage  in  the  term  skeleton), —  an 
arch  within  an  arch,  an  internal  cartilaginous 
and  an  external  osseous  one.  (Figs.  9  and  l" 
represent  one  of  its  bi-sections.) 


Fl«-  10-  I  i...     10.  -  Internal 

face  of  the  right  in- 
ferior maxilla  of  a  hu- 
man embryo  of  about 
three  months,  showing 
the  natural  size  and 
the  relative  position  of 
Meckel's  cartilage :  as 
also  the  dental  follicles, 
from  which  the  internal  face  of  the  bone  is  lifted  off: 
a.  the  extra-tympanic  portion,  often  flexible  beyond  the  ori- 
fice of  the  dental  canal;  h.  the  symphysis  of  the  cartilage; 
n,  the  manubrium  mallei  (or  handle  of  the  hammer),  with 
a  little  fibrous  prolongation ;  c,  the  cartilage  of  the  incus 
(or  anvil).  This  figure  represents  the  internal  surface  of 
Meckel's  cartilage,  or  the  interior  of  the  arch.  (Magitot  and 
Robin). 

In  an  anatomical  view  this  cartilage  consists 
of  two  parts  —  a  transitory  maxillary,  or  ex- 
tra-tympanic,  and  a  persistent  auricular  part. 
The  former,  after  it  is  no  longer  needed  to  bus-  ■ 
tain  the  jaw,  begins  to  waste  away :  while  the 
latter,  which  represents  the  malleus,  gradually 
becomes  ossified. 


36 


TRANSLATOR  8    INTRODUCTION. 


Fig.  11. 


Fig.  11.  — Meck- 
el's cartilage,  from 
a  human  embryo  of 
forty  to  forty-two 
days,  and  before  the 
appearance  of  the 
maxillary  bone; 
magnified  twenty- 
five  diameters.  af 
Enlargement  of  the. 
cartilage  near  its 
union  with  the  neck 
of  the  malleus ;  br 
a  slightly  enlarged 
portion  of  the  car- 
tilage in  the  form  of 
a  spatula,  but  con- 
tracted at  the  me- 
dian line,  where  it 
unites  with  that  of 
the  opposite  side ; 
m,  head  of  the  mal- 
leus ;  n,  handle  of 
the  malleus;  e,  car- 
tilage of  the  incus; 
o,  cartilage  of  the 
os  lenticulare ;  I, 
cartilage  of  the 
stapes.  [The  outline 
of  a  jaw  has  been 
added  to  this  figure 
to  show  the  relative 
position  it  will  oc- 
cupy when  ossifica- 
tion takes  place.] 
(Magitot  and  Robin. )■ 


\n:<  kel's  cartilage.  37 

This  (tssiiicitinii  ut"  the  auricular,  and  absorp- 
tion of  the  transitory,  portions  commence  al  the 
end  of  the  third  month  of  intra-uterine  life;  the 
former  with  the  malleus,  the  latter  at  points 
corresponding  with  the  middle  portion  of  each 
jaw.  whence  atrophy  extends  in  both  directions; 
and,  toward  the  latter  part  of  the  sixth  month. 
according  to  these  authors,  the  cartilage,  from  the 
simphysis  to  the  malleus,  entirely  disappears, 
leaving  for  a  time  on  the  surface  of  the  bone  a 
slight  groove  to  mark  the  place  it  occupied. 

Frank  :  I  infer  that  Meckel's  cartilage  belongs 
exclusively  to  the  lower  jaw  of  the  human  foetus. 

Teacher:  It  is  by  no  means  the  exclusive 
heritage  of  man.  All  the  different  species  of 
mammals,  reptiles,  fishes,  and  even  birds,  in  em- 
bryonal  life  possess  this  transitory,  cartilaginous 
support  to  the  lower  jaw.  But  it  does  not  in 
all  these  disappear  (as  it  does  in  main  before 
birth.  In  the  rodents, — rats  and  mice,  for  ex- 
ample,— it  remains  without  sensible  change  till 
birth,  or  a  little  later. 

This  brief  description,  aided  by  these  excel- 
lent cuts,  will,  I  hope,  give  you  a  sufficiently 
accurate  idea  of  this  cartilage  to  satisfy  you  for 
the   present.     But  if  you    desire    further    infor- 


38         translator's  introduction. 

mation.  I  must  refer  you  to  the  thoroughly 
exhaustive  treatise  already  alluded  to ;  *  for  I 
know  of  no  comparatively  complete  work  upon 
this  subject  in  the  English  language. 

§  III.— INTER-MAXILLARY  BONES. 

Casper  :  There  is  another  obscure  point  that 
I  would  like  to  have  cleared  up  before  it  escapes 
my  mind.  In  your  remarks  you  have  referred 
to  the  origin  of  the  "  mfer-maxillary  bones."  I 
was  not  aware  that  any  such  exist  in  the  human 
skeleton.  Our  medical  and  dental  text-books 
say:  "The  maxillary  bones  are  two  in  number, 
united  on  the  median  line  of  the  face."  If 
this  be  so,  where  can  we  locate  the  inter- 
■  maxillae  ? 

Teacher  :  The  reason  why  your  text-books 
do  not  describe  these  bones  is,  probably,  because 
the  authors  recognize  their  .existence  only  in 
early  foetal  life,  and  hence  do  not  deem  it  neces- 
sary. But  naturalists  consider  them  very  im- 
portant features  in  zoological  science,  since  the 
point  where  they  unite  with  the  maxillae  forms 

*  See  Memoire  sur  un  Organe  Transitoire  de  la  Vie  Fcetale, 
de"signe  sous  le  nora  de  Cartilage  de  Meckel.  (E.  Magitot 
et  Ch.  Robin.     Paris,  1862.) 


INTKKMAXILLAKY     I '.ONES.  39 

the  dividing  line  between  the  incisor  and  canine 
teeth.  It  seems  to  me  that  an  intimate  knowl- 
edge of  these  parte  is  essential  to  a  thorough 
education  in  general  medicine,  and  especially  in 
the  department  of  dental  surgery. 

In  foetal  life  the  upper  jaw  is  composed  of 
four  bones,  viz.,  two  maxillary  and  two  inter- 
maxillary. In  each  of  the  latter  will  be  devel- 
oped and  supported  two  incisors  —  a  central 
and  a  lateral;  in  each  of  the  former,  one  cuspid 
and  all  the  teeth  posterior  to  it. 

Although  the  intermaxilhe  are  distinct  bones 
in  the  human  fetus,  their  external  surface  is 
soon  covered  over  with  a  process  from  each  max- 
illa, which  extends  toward  the  median  line,  and 
becomes  intimately  fused  with  the  former  before 
birth;  so  that  the  intermaxillary  suture  cannot 
be  seen  on  the  outer  side ;  but  on  the  palatal 
aspect  of  these  bones  the  suture  can  always  be 
recognized  at  birth,  and  can  often  be  traced 
even  in  adult  life.     (Flowers,  Linnaeus   Martin.) 

In  many  animals  these  remain  permanently 
as  separate  bones;  and  in  human  subjects,  where 
the  jaw  is  malformed,  detached  pieces  are  often 
found  in  this  situation,  probably  owing  to  their 
arrested  development.     (Gray.) 


40 


TRANSLATOR  S    INTRODUCTION. 


By  Huxley,  and  many  other  authors,  these 
bones  are  called  the  premaxillce  •  these  parts 
are  also  known  as  the  incisive  region,  from  the 
fact  that  the  incisor  teeth  are  implanted  in 
these  bones.* 


Fig.  11. 


Fig.  11. —  From  a  foetus  of 
about  four  months;  showing  the 
palatal  aspect  of  the  inter-max- 
illary bones,  and  indicating  the 
points  that  will  be  occupied  by 
the  teeth  when  developed;  also 
the  inter-maxillary  suture  sep- 
arating the  canine  and  incisor 
teeth. 


*  Perhaps  it  is  due  to  the  reader  that  I  here  state  that 
the  existence  of  these  bones  in  the  human  skeleton  is  not 
an  altogether  uncontroverted  question.  I  had  prepared  a 
somewhat  extended  article,  giving  a  sketch  of  the  treat- 
ment this  subject  has  received  from  the  pens  of  many 
anatomists  and  naturalists,  from  the  days  of  G-alen  to  the 
present.  But  on  reflection  I  have  concluded  to  suppress 
it,  together  with  much  other  collateral  matter,  lest  the 
work  should  be  so  much  cumbered  thereby  as  to  render 
it  tiresome  or  confusing  to  the  student.  The  fact,  however, 
stands  unshaken,  (as  stated  by  Prof.  Paul  Gervais,  in  his 
work  on  the  human  skeleton,  Paris,  1856,)  that  Vicq- 
d'Azyr  and  Goethe  have  shown  that  these  bones  exist  in 
the  human  species,  as  well  as  im  all  the  other  mammalia. 
The  thought  that  Goethe,  the  great  poet  and  naturalist, 
has  made  these  little  bones  the  object  of  special  scientific 


DEFINITION    OF    TERMS.  41 

§ IV.— DEFINITION  OF  THE  TERMS    FCETUS,    EM 
BRYO,  FOLLICLE  AM'  BOURGEON. 

Frank:  I  notice  thai  sometimes  yon  employ 
the  term  embryo  and  sometimes  fcetw.  I  sup- 
pose they  have  the  same  meaning? 

Teacher:  Magitot,  Kolliker,  LegroB,  Frey, 
Gray,  and  many  other  reputable  authors,  use 
these  terms  indiscriminately,  as  words  of  the 
same  signification.  On  the  other  hand,  Dungli- 
son,  Palmer,  Carpenter,  Flint,  and  others,  employ 
the  term  embryo  to  designate  the  rudimental  be- 
in--  during  the  first  four  months  of  intrauterine 
life,  after  which  they  style  it  the  foetus.  Some 
again  (including  some  of  the  last-named  au- 
thors) divide  the  period  of  gestation  into  three 
stages.  In  the  first  the  germ  is  called  an  ovum.; 
when   this  begins  to  assume  the  appearance  of 

study  may,   in  the  minds  of  some,    lend  a  charm   to  this 
subject  that  it  would  not  otherwise  possess. 

It  cannot  he  doubted,  I  think,  that  these  bones  originate 
from  separate  points  of  ossification;  but  they  certainly,  a* 
a  rule,  become  fused  with  the  maxillary  bones,  on  the 
external  surface,  at  a  very  early  period  of  fietal  life,  some- 
times before  the  fifth  month;  while  on  the  palatal  aspect 
the  suture  is  often  distinct,  extending  across  the  external 
alveolar  process  after  birth. 
4 


42         translator's  introduction. 

a  body,  it  is  termed  an  embryo  /  and  about  the 
end  of  the  fourth  month  (the  time  corresponding 
to  the  period  of  "  quickening ")  it  is  accorded 
the  name  of  foetus,  which  designation  it  retains 
until  birth. 

This  application  of  the  two  latter  terms  to 
different  periods  of  gestation  is  entirely  arbi- 
trary, and  in  some  respects  objectionable;  but 
I  shall  generally  adopt  it,  since  it  possesses  some 
advantages.  But  sometimes  it  will  be  almost 
unavoidable  to  speak  of  embryonal  or  foetal  life, 
as  equivalent  to  intrauterine  life. 

Frank:  While  you  are  defining  terms  I 
would  like  to  know  just  what  our  authors  mean 
by  "dental  follicle." 

Teacher  :  The  dental  follicle  includes  the 
following  parts:  the  dentine-bulb  (papilla),  the 
enamel-organ,  and  the  sac  that  envelops  them 
which  is'  called  the  follicular  wall.  These  three 
parts  constitute  the  dental  follicle. 

The  word  follicle  is  not  used  here  in  its 
primary  signification  —  a  little  bag  or  sac  —  but 
as  a  sac  and  its  contents.  Kolliker  employs 
an  equivalent  expression,  dental  sacculus,  in  the 
same  sense.  This  word  follicle  is  also  simi- 
larly employed   by  many  other  anatomists, —  as 


DEFINITION    <»F    TERMS. 


4-'i 


"Graafian  follicle,"  "Malpighian  follicle,"  etc. 
Tomes,  and  English  and  American  writer.-  gen- 
erally, ose  tin'  terms  follicle,  Bac,  and  capsnle,  as 
words  of  the  same  meaning.  It  is  unfortunate 
that  BOme  definite  and  universal  term  is  not  em- 
ployed to  designate  these  associated  parts  of  the 
developing  tooth  ;  but  for  want  of  such,  I  shall 
retain  the  term  follicle  in  the  sense  that  it  is 
used  by  the  authors  of  this  work.  (Fig.  12  very 
well  represents  a  dental  follicle.) 


Fig.  12.  — This 
cut  is  taken  from 
the  fifth  edition  of 
Kolliker's  HistoVy. 
Though  the  enamel 
and  dentine  are  al- 
ready pretty  well 
developed,  the  mass 
represented  by  the 
figure  is  still  a  den- 
tal follicle.  It  is 
from  a  feline  em- 
bryo magnified 
fourteen  diameters. 
a,  Dentine-bulb;  e, 
enamel  -organ  ;  //, 
follicular  wall. 


44         translator's  introduction. 

Frank  :  Now,  one  question  more.  You  used 
the  term  "  bourgeon  "  several  times  during  your 
description  of  the  development  of  the  jaws.  It 
is  not  a  familiar  word  to  me,  though  I  suppose 
it  means  about  the  same  as  process. 

Teacher  :  The  word  means  bud.  germ,  shoot, 
or  sprout;  and  the  primitive  outgrowths  are 
called  bourgeons,  apophyses,  processes,  etc.  It 
is  a  French  word,  but  has  become  Anglicized, 
and  may  be  found  in  your  English  dictionary. 
This  term  is  often  employed  in  the  text  as  sig- 
nifying enamel-germ,  or  enamel-bud.  When  the 
buddings  take  place  which  develop  into  enamel- 
organs,  these  offshoots  or  buds  are  denominated 
bourgeons  of  the  enamel-organ,  or  simply  bour- 
geons. 

I  cannot  close  these  introductory  remarks 
without  a  word  of  apology  for  the  term  "cell," 
which  has  been  used  so  freely  in  the  foregoing 
pages.  Now  although  this,  or  its  equivalent, 
zellen,  cellule,  or  cella,  has  been  almost  univer- 
sally adopted  by  anatomists,  the  word,  as  applied 
by  them,  is  manifestly  a  misnomer.  And  yet  its 
primitive  signification,  as  first  used  by  Schleiden, 
has  been  so  modified  from  time  to  time,  to  cor- 
respond with  our  clearer  conception  of  the  mor- 


i»i;i  IM  i  ion    OF   TERMS.  45 

phology  and  nature  of  the  little  mass  of  matter 
1 1 1 1 1 >  designated,  that  it  will  require  greal  philo- 
logical research  to  discover  a  substitute  which 
will  be  as  definite  and  comprehensive  as  this 
term,  thus  modified,  has  now  become.  Never- 
theless, it  is  a  stumbling-block  to  the  student, 
and  is  an  example  of  the  many  defects  in  our 
terminology,  that  a  tew  scientists,  prominent 
among  whom  I  may  name  Dr.  Atkinson,  of 
New-  York,  are  making  praiseworthy  efforts  to 
remedy. 

With  a  few  preliminary  remarks  from  our 
authors,  we  shall  now  he  introduced  into  our 
main,  and   most   interesting,  field  of  study. 


THE  AUTHORS'   INTRODUCTION. 


TIIK  work  we  publish  to-day  comprises  the 
first  part  of  a  series  of  studies,  which  em- 
brace the  entire  phenomena  of  the  evolution  of 
the  dental  system  of  mammals. 

This  subject,  which,  as  you  are  aware,  is 
one  of  the  most  difficult  that  we  have  to  en- 
counter in  embryology,  and  which  is  still  in- 
volved in  very  great  obscurity,  has  been  made 
bv  us  the  field  of  extensive  investigations, 
both  on  the  human  embryo  and  on  those  of 
the  domestic  animals.  By  these  studies  we  have 
been  convinced  that  the  phenomena  presented 
in  the  series  of  raamraifera  have  (except  in  a 
few  minor  differences)  a  perfect  similarity  in 
their  general  physiological  facts;  the  develop- 
ment of  the  follicle,  the  anatomical  composition 
of  its  parr-,  ami  the  role  which  these  perform 
in  the  functions  of  the  dental  organism,  are  in 
all  respects  similar. 

Our  researches  in  this  direction  have  been 
stimulated  not  solely  by  the  state  of  uncertainty 
and  of  controversy    in   which    this   question   is 


48  THE   AUTHOKS'    INTRODUCTION. 

involved,  but  also  by  the  perusal  of  several  im- 
portant works  published  of  late  years  in  Ger- 
many by  different  anatomists, —  Kolliker,  Wal- 
deyer,  Hertz,  Kollmann  and  others. 

The  results  presented  by  these  observers  have 
gained,  for  certain  parts  of  the  question,  consid- 
erable importance.  They  have  determined  some 
new  elements  that  are  a  legitimate  acquisition 
to  science;  while  other  conclusions  which  tend 
to  invalidate  certain  doctrines  advanced  by  sev- 
eral English  and  French  authors,  lack,  as  we 
shall  endeavor  to  show,  sufficient  precision  and 
exactness.  Besides,  there  are  several  questions 
which  remain  without   any  solution  whatever. 

It  is  with  the  hope  of  throwing  light  upon 
this  problem,  that  we  have  undertaken  this 
series  of  researches. 

Following  rigorously  the  physiological  order, 
we  have  been  led  to  consider  successively : 

1.  The  mode  of  origin  and  formation  of  the 
dental  follicle.  2.  The  morphology  and  struct- 
ure of  that  follicle  at  the  period  of  its  complete 
development.  3.  The  evolution  of  the  tooth 
within  the  follicle. 

The  present  memoir  will  be  devoted  to  the 
consideration  of  the  [two]  first  of  these  questions. 


THE  OliUJIX  AND   FOLIATION 


DENTAL  FOLLICLE 


CHAPTER   I. 


THE  CONDITION  OF  TIIK  JAWS  OP  THE  EMBBYO  AT  THE 
PERIOD  OF  THE  (JENESIS  OK  THE  FOLLICLE.  THE 
EPITHELIAL   RIDGE   i  BOVRRELET). 


T 


IIIOUGII  we  do  not  intend   to  dwell 

-1-  long  upon  the  general  constitution  of 
tlif  jaws  at  the  time  of  the  genesis  of  the 
follicle,""  still  we  think  we  ought  to  lay 
special  stress  upon  certain  points  which  are 
directly  connected  with  our  subject. 

A-  regards  the  lower  jaw,  it  is  known 
that  at  a  certain  epoch  in  embryonal  lite, 
varying  according  to  the  species  of  animals, 
the  maxillan  arch,  absolutely  destitute  of 

*  See  Memoir  on  the  Genesis  and  Development  of  the 
Dental  Follicles,  by  Ch.  Robin  ami  E.  Magitot;  in  the  physio- 
logical journal  of  Brown-S6quard,  1800. 


50  THE    ORIGIN    AND    FORMATION 

the  least  trace  of  osseous  tissue,  incloses 
within  its  component  elements  a  symmetri- 
cal cartilaginous  band ;  and  that  this,  unit- 
ing with  its  fellow  at  the  median  line,  or 
the  future  symphysis,  extends  not  only  the 
whole  length  of  the  maxillary  arch,  but 
even  to  the  frame  of  the  tympanum. 

This  is  Meckel? s  Cartilage, —  an  organ 
which  plays  only  a  transitory  part  in  the 
development  of  the  maxilla,  and  occupies 
the  interior  part  of  the  arch.  Thus  embed- 
ded within  the  embryonic  tissue,  it  repre- 
sents, at  this  epoch  of  intrauterine  life,  the 
only  fundamental  elements  of  the  jaw. 
(Figs.  8,  9  and  10,  pp.  33-4-5.) 

As  to  the  upper  jaw,  the  period  of  evo- 
lution corresponding  with  that  which  we 
have  just  described  in  the  lower,  is  that  at 
which  the  maxillary  bourgeons  have  united 
with  the  median  or  intermaxillary  bour- 
geon.*     This  phenomenon  takes  place  in 

*  [These  authors  speak  of  the  two  maxillary  bourgeons  as 
uniting  with  the  median  or  intermaxillary  bourgeon.  From 
this  it  would  be  inferred  that  there  was  but  one  intermaxil- 


oi     THE    DENTAL    FOLLICLE.  51 

the  human  embryo  about  the  fortieth  or 
forty-fifth  day. 

The  two  maxillary  arches  being  thus 
formed,  we  soon  obsen  e  thai  in  the  rounded 
part  (which  will  afterward  constitute  the 
alveolar  border),  there  is  produced  a  bed 
of  epithelial  cells  forming  a  protuberance 
or  smooth  ridge  (saUlii  ou  bowrrelet),  and 
without  any  fold  or  depression  whatever. 
This  ridge,  visible  to  the  naked  eye,  is  still 
more  manifest  in  a  section  cut  perpendicu- 
lar with  the  axis  of  the  maxillary  arch,  and 
is  composed  of  a  thick  bed  of  cells.  It  will 
he  noticed  that  on  its  sides  an  epithelial 
coat  is  formed  of  only  a  few  rows  (rangees) 
of  these  cells,  superposed  upon  each  other; 
and   sometimes,  even  of  a   single  row. 

The  epithelial  ridge  is  thus  added  to  the 
embryonal  elements  before  fchej  include  any 

lury  bourgeon.  They  use  the  singular  number  here,  prob- 
ably because  these  bourgeons  have  already  formed  a  union 
at  their  external  margins,  which  connection  takes  place  a 
little  before  their  union  with  the  maxillary  bourgeons.— See 
Robin  ami  Rfagitot,  loc  cit..  p.  9. — Tr.] 


52  THE    ORIGIN    AND    FORMATION 

other  well  defined  tissues,  unless  it  "be  some 
vessels,  nerves,  and  muscle-fibres,  in  process 
of  evolution. 

This  epithelial  ridge  has  some  peculiari- 
ties which  are  of  sufficient  importance  to 
demand  our  special  attention,  and  which 
one  would  not  suspect  from  simply  examin- 
ing its  buccal  or  exterior  surface.  In  a 
vertical  section  you  will  notice  the  smooth 
and  rounded  ridge  that  it  presents  in  the 
mouth,  and  which  justifies  the  name  we 
give  it  —  maxillary  rampart  (Kieferwall 
of  Kolliker,  Waldeyer  and  Kollmann). 

Fig.  13.  Fig.  13. — From  Thiersch's  prepa- 

ration of  an  embryonic  pig  (copied 
from  Frey).  d,  A  mass  of  epithe- 
lium —  the  ' '  dental  ridge, "  "  max- 
illary rampart  "  or  "  Kieferwall 
(represented  by  the  same  letter  in 
the  preceding  and  following  cuts); 
b,  younger  layer  of  epithelium;  c, 
the  deepest  layer  —  the  prismatic  or 
columnar  stratum;  e,  enamel-germ. 

Beneath  this  external  ridge  a  projection 
sinks  into  the  subjacent  elements,  the  out- 
lines of  which   represent  nearly  the  form 


e-^m 


OF    THE    DENTAL    FOLLK  i.i  .  53 

of  the  letter   I  .  wit  1 1  the  apex  slightly  in- 
clined toward  the  inner  side  |  Fig.  14,  d,  <1 ). 

PlO.    II. 


-il?t  *••■»*:;"," 


Fig.  14. — A  perpendicular  section  taken  from  the  inci- 
sive region  of  the  lower  jaw  of  an  ovine  embryo  (lamb), 
forty-two  millim.  in  length  (magnified  eighty  diameters.) 
d,  '/.  Kpithelial  band  Q>ourrelet)\  <<,  ".  transverse  section  of 
Meckel's  cartilage  near  the  symphysis:  c,  c,  depression  of 
the  mucous  membrane;  c,  section  of  the  tongue.  (See  same 
letters  Fig.  7,  p.  30.) 

Casper:    I  cannot  see  the  appropriateness  of 

the  term  "epithelial  ridge"  which  is  used  so 
often.  In  tin1  plate  it  looks  more  like  a  groove 
than  a  ridge. 

Teacher:  This  term  does  not,  to  my  mind, 
express  definitely  the  thick  epithelial  bed,  which, 
though  it  presents  on  the  external  surface  of  the 


54  THE    ORIGIN    AND    FORMATION 

jaw  an  eminence  or  ridge,  yet  sinks  into  the 
substance  of  the  jaw  to  a  greater  depth  than  it 
rises  above  the  general  surface.  The  word 
used  by  the  authors  is  bourrelet,  which  means 
a  rounded  pad,  or  cushion.  This  structure  was 
for  a  long  time  supposed  to  be  cartilaginous  in 
its  nature,  and  hence  called  cartilago  dentalis, 
until  Raschkow  discovered  its  epithelial  charac- 
ter. M.  Guillot  (1859)  named  it  the  odontogenic 
part,  or  the  generating  part  of  the  teeth ;  our 
authors  speak  of  it  frequently  as  an  epithelial 
band,  and  we  will  hereafter  so  denominate  it. 

In  a  vertical  transverse  section  this  band  is 
represented,  as  has  been  stated,  by  the  letter  V, 
with  the  apex  bent  a  little  inward.  Now  fill 
this  with  epithelial  cells,  and  heap  them  up, 
and  you  have  a  tolerably  accurate  idea  of  the 
epithelial  bourrelet  or  band.  In  other  words, 
make  a  groove  the  entire 
length  of  the  jaw,  shaped* 
as  just  described,  and  fill  it 
"  heaping  full "  of  this  cel- 
lular mass,  and  it  also  will 
represent  the  epithelial  band, 
as  seen  in  fig.  15. 


OF   THE    DENTAL    FOLLICLE.  f>5 

Thus  constituted,  the  hourrelei  forms, 
in  reality,  ;i  continuous  epithelial  band, 
Dearly  vertical,  the  whole  Length  of  the 
alveolar  border.  It  always  exists  in  the 
embryos  of  man  and  the  higher  mammalia, 
and  is  even  found  on  some  parts  which 
will  remain  devoid  of  teeth,  as  in  the  bar 
of  the  solipeds. 

Frank:  "The  bar  of  the  solipeds"  is  too 
much  for  me;  soliped,  single  foot.  I  did  not 
know  there  were  any  one-footed  animals! 

Caspki;  :  I  know  that  the  name  soliped  is 
applied  to  the  races  of  animals  that  have  a  single 
hoof — as  the  horse  and  ass  —  but  I  am  stuck 
on  the  "bar." 

Teacher:  In  animals,  that  interval  between 
the  "tusks"  and  the  molars,  which  is  destitute 
of  teeth,  is  technically  called  the  bar;  and 
though  the  band  extends  along  this  portion  of 
the  jaw,  it  is  unproductive,  and  becomes  atro- 
phied and  absorbed,  as  we  shall  see  further  on. 
The  more  elegant  term  Hiasti'ina  is  quite  com- 
monly employed  to  denote  this  vacant  space  be- 
tween the  teeth  of  the  soliped,  as  well  as  those 
that  may  occur  in  the  jaws  of  other  animals. 


56  THE    ORIGIN    AND    FORMATION 

I  will  give  you  the  substance  of  a  very  inter- 
esting foot-note  from  the  pen  of  Dr.  Pietkiewicz 
(a  former  pupil  in  the  laboratory  of  Prof.  Robin) 
on  the  Rudimentary  Dental  Organs  of  the  Rumi- 
nants. It  has  been  inserted  here  with  the  in- 
dorsement of  the  authors  of  this  work ;  but 
owing  to  its  great  length  1  shall  give  only  a 
brief  summary  of  its  contents,  as  published  in 
the  "Transactions  of  the  American  Dental  Asso- 
ciation,".1878 : 

You  are  aware  that  there  is  a  wide-spread  belief,  which 
had  its  origin  in  the  announcement  of  Goodsir,  in  1839, 
that  rudimentary  incisor  teeth  may  be  found  in  the  em- 
bryonal jaws  of  Ruminants.  This  statement,  founded  upon 
certain  anatomical  appearances,  was  seized  upon  by  Darwin, 
Hseckel,  and  other  scientists,  to  sustain  their  views  regard- 
ing- the  changes  that  had  taken  place  in  the  successive 
generations  of  animal  beings;  and  thus  the  theory  received 
additional  credit  and  a  fresh  impulse,  until  it  has  now 
become  the  prevailing  belief,  that  the  upper  jaws  of  the 
fcetus  of  ruminants  contain  germs  of  teeth;  which,  however, 
disappear  before,  or  soon  after,  the  birth  of  the  animal. 

This  conclusion  of  Goodsir,  which  was  never  carefully 
verified,  has  recently  been  severely  shaken,  if  not  entirely 
overthrown,  by  the  researches  of  Dr.  Pietkiewicz. 

He  says,  that  in  attempting  to  verify  the  statement  of 
Goodsir,  which  had  obtained  such  extensive  circulation 
and  credit,  he  made  experiments  upon  a  series  of  embryos 
of  cattle  and  sheep,    taken  in  large  numbers,   from   the 


of    l  III     DENTAL    FOLLICLE.  57 

earliest  period  of  intrauterine  life  until  they  bad  attained 
thirty  centimeters,  or  one  foot,  in  length.  In  this  series 
of  investigations,  be  ooi  only  never  witnessed  the  presence 
of  a  dental  germ,  but  never  found  even  a  trace  of  the 
epithelial  lamina. 

He  further  states,  however,  thai  in  the  commencement 
of  his  work  he  was  led  into  an  error  by  the  deceptive  ap- 
pearance of  the  sections  made  entirely  from  the  anterior 
portion  of  the  jaws;  for  in  these  he  found  on  each  side  of 
the  median  line  an  epithelial  sac,  which  extended  from 
the  mucous  membrane  into  the  depth  of  the  jaw,  and  which 
appeared  to  constitute  the  commencement  of  dental  germ-. 
such  as  Goodsir  undoubtedly  conceived  them  to  be.  No 
difference  was  observed  between  the  epithelium  of  this  sac 
and  that  of  the  mucous  membrane,  of  which  it  appeared 
to  be  a  depression.  The  Malpighian  layer  constituted  its 
outer  investment,  while  in  its  interior  was  found  paviment- 
ous  epithelium. 

From  this  appearance,  he  thought  one  could  easily 
conceive  how  Goodsir  might  have  been  led  into  the  belief 
that  he  had  discovered  dental  germs.  But  in  continuing 
to  make  sections  from  these  jaws  in  a  posterior  direction, 
he  found  that  the  little  sac  assumed  the  form  of  a  circular 
canal,  and  approached  the  mucous  membrane  of  the  nasal 
fossa-.  Around  this  canal  appeared  a  cartilaginous  cornet, 
and  in  the  upper  part  was  a  mass  containing  vessels.  From 
this  he  recognized  the  organ  of  Jacobson.  There  was  ab- 
solutely nothing,  he  says,  that  could  be,  even  remotely, 
compared  to  the  germs  of  the  incisor  or  canine  teeth. 
5 


58  THE    ORIGIN    AND    FORMATION 

The  form  of  the  epithelial  Land  is  the 
same  in  the  different  species  of  animals; 
and  while  it  presents  its  broadest  aspect  on 
the  alveolar  ridge,  it  grows  thinner,  and  at 
the  same  time  bends  a  little  inward,  as  it 
descends  into  the  subjacent  tissues ;  so  that 
its  internal  or  lingual  face  presents  a  con- 
cavity, and  its  labial  or  buccal  face  a  con- 
vexity. 

Though  the  deeper  extremity,  or  apex,  of 
the  band  is  blunt  and  rounded  in  the  early 
stage  of  development,  it  becomes  very  sharp 
at  the  moment  the  first  trace  of  the  follicle 
appears. 

This  band  is  composed  of  the  same  histo- 
logical elements  that  constitute  the  epithe- 
lial coat  of  the  oral  mucous  membrane, — 
that  is  to  say,  of  nucleated  cells,  rendered 
polyhedral  in  form  by  reciprocal  pressure ; 
and  that  portion  which  penetrates  the  tis- 
sues of  the  jaw  is  bounded  by  a  continuous 
layer  of  prismatic  cells.  The  cells  that 
compose    the    center    of    the    band    often 


OF    THB    DENTAL    loi.LiCLK. 


(9 


l'i...   15. 


present  .-it   their  borders  thai   denticulated 
arrangemenl    which     has 
been  noticed   by  authors 

in  the  cells  of  the  epi- 
dermis, and  by  which  the 
elements  interlock  with 
each  other.  [Cells  described  in  the  Intro- 
duction, as  the  "imbricated,"  "  prickle,"  etc., 
to  which  list  we  will  add  here  the  explica- 
tives  "thorny"  and  "heckle."  Fig.  15.] 
fi... jB.  As  regards  the  prismatic 

layer,  it  «lnes  ii»i  differ 
^s  from  the  stratum  Mai- 
d  -■^^  /'/<////>,  from  which  it  is 
directly  derived.  [Fig.  16,  b.  From  F)'ey.~\ 
From  the  preceding  considerations  it  is 
seen  that  the  epithelial  band,  which  we 
have  jusl  described,  is  simply  a  prolongation 
of  the  epithelial  tegumentary  layer  {couch.  ) 
of  the  mouth,  which,  in  sinking  into  the  em- 
bryonic tissues  of  the  jaws,  forms  for  itself, 

SO  to  -peak,  a  groove  which  it  exactly  tills. 

N<>\\.  when   the  embryonal  jaw  is  sub- 


60  THE    ORIGIN    AND    FORMATION 

jected  to  a  prolonged  maceration,  the  band 
may  become  spontaneously  detached,  thus 
leaving  an  empty  groove ;  but  at  no  epoch, 
in  embryonal  life,  can  there  be  found,  on 
the  surface  of  the  alveolar  border,  any  de- 
pression, sinking,  or  perforation  whatever, 
when  these  parts  are  in  a  normal  condition. 
The  well-known  theory  of  the  evolution 
of  the  teeth  advanced  by  Goodsir  in  1837, 
and  afterward  adopted  by  most  authors, 
was  founded  on  a  certain  mechanism,  which 
consisted  in  the  formation  of  the  follicular 
sac  at  the  expense  of  an  exterior  depression 
of  the  oral  mucous  membrane.  The  detach- 
ment  of  the  epithelial  bed  by  maceration 
may,  doubtless,  account  for  this  tSror;  but 
nothing  exists  in  the  normal  state  of  the 
jaws  to  warrant  any  such  conclusion.  The 
theory  of  Goodsir  is,  therefore,  absolutely 
without  foundation  in  fact.* 

*  [For  a  long  time  Goodsir's  theory  of  the  evolution  of 
the  teeth  was  held  to  be  correct,  and  his  verbal  and  pic- 
torial representations  were  copied  into  our  standard  text- 
books on    anatomy    and    physiology,    both    medical    and 


OF    THE    DENTAL    FOLLICLE.  <>1 

dental;  and  even  Kdlliker,  up  to  his  fourth  edition,  bor- 
rows from  that  author  tin-  cuts  illustrating  this  stage  of 
.■volution,  (ioodsir  "  believed  that,  at  an  early  period  of 
total  life,  there  appears  a  continuous  open  groove,  run- 
ning round  the  whole  circumference  of  the  jaws;  that  from 
the  bottom  of  this  groove  there  arose  isolated  and  un- 
covered papillae,  corresponding  in  number  to  the  milk 
teeth;  that  these  papilla'  become  covered  in  by  the  deepen- 
ing of  the  groove  and  the  meeting  of  its  two  edges  over 
their  tops,  whilst  at  the  same  time  transverse  septa  were 
formed,  so  that  the  several  papillae  become  enclosed  in 
their  own  separate  follicles." — Tonus'  Mux.  of  Doit.  A  nut. 
"  This  theory  of  Goodsir  was  vigorously  attacked  at  a 
later  date  in  works  of  the  French  histologists  Guillot,  and 
Magitot  and  Robin.  According  to  the  latter,  the  tooth - 
sacs,  dental  germs,  and  remaining  parts  are  developed,  in 
the  first  instance,  within  the  submucous  connected  tissue 
(subdermis),  quite  independent  of  the  epithelium  or  mu- 
cosus." — F  ni/.    Tk.] 


62  THE    ORIGIN    AND    FORMATION 


CHAPTER  II. 


THE  EPITHELIAL  LAMINA,  AND  THE  GENESIS  OF  THE 
ENAMEL-ORGAN. 

"TTTE  have  seen  that  the  part  of  the 
•  *  epithelial  bourrelet,  or  band,  which 
sinks  into  the  tissue  of  the  jaw,  presents 
two  faces  —  an  external  convex  and  an  in- 
ternal concave  one;  and  that  it  extends 
the  entire  length  of  the  alveolar  border. 
Now,  as  soon  as  the  development  of  this 
organ  is  completed,  a  thin  process  shoots 
out  from  its  internal  face,  which  we  shall 
designate  the  epithelial  lamina.  (Figs.  17 
and  18,  E  E.) 

This  lamina  is  a  continuous  process,  ex- 
tending the  whole  length  of  the  epithelial 
band,  from  which  it  emanates  about  mid- 
way between  its  apex  and  the  epithelial 
layer  (sometimes  a  little  nearer  the  latter) r 


OF    THE    DENTAL    I  OLLIOLE.  63 

and    appears   t<>    be   a    kind   of  diverticu- 
lum (or  inflexion)  of  the  band   itself..   It 

Fio.  17. 


Fig.  17. — A'ertical  section  of  the  anterior  portion  of  the 
lower  jaw  of  an  ovine  embryo  measuring  59  millimetres. 
a.  Showing  the  section  of  Meckel's  Cartilage;  d,  epithelial 
band  (or  bourrelet);  c,  fold  in  the  mucous  membrane;  E, 
epithelial  lamina.  These  letters  refer  to  the  same  parts  in 
the  foregoing  and  following  figures. 

is  somewhat  flattened  from  above  down- 
ward, and  it-  rounded  extremity  is  slightly 
bent  in  the  form  of  a  crosier.  (  Fig.  18,  E. ) 
The  elements  of  tin*  lamina  are  of  the 
same  character  as  those  which  compose  the 
band,  viz.,  polygonal  cells  inclosed  1>\  a  con- 
tinuous layer  of  prismatic  cells.  As  develop- 
ment advances,  Large  polygonal  cells  make 
their  appearance  in  the  thicker  portion  of 


64  THE    ORIGIN    AND    FORMATION 

the  lamina,  similar  to  those  found  in  the 
band,  or  external  epithelium.  These  ar- 
rangements are  important  to  be  noticed ; 
for,  as  will  be  seen  hereafter,  the  prismatic 

Fia.  18. 


,===wi,=-sCL 


■M 


Fig.  18. —  Transverse  section  of  the  left  branch  of  the 
lower  jaw  of  an  ovine  embryo  (65  millimetres  in  length), 
magnified  260  diameters.  This  and  the  preceding  cut  show 
the  arrangement  of  the  elements  of  the  epithelial  band,  and 
also  the  epithelial  lamina. 

d,  Epithelium  of  the  mucous  membrane,  extending  nearly 
vertically  into  the  jaw  and  constituting  the  band  and  the 
lamina.  E,  Epithelial  lamina,  emanating  from  the  band. 
The  band  and  lamina  are  surrounded  by  the  embryonal 
tissue  of  the  jaw.  This  portion  of  the  engraving  is  faulty, 
in  that  the  nuclear  elements  are  lighter  than  the  surround- 
ing mass,  whereas  they  should  appear  darker, 


(il     THE    DENTAL    FOLLICLE.  65 

elements  which  form  its  outer  investment 
arc  never  found  in  the  debris  of  the  Lamina, 
nor  in  those  of  the  epithelial  cord  which  is 
derived  from  it. 

The  t  ilium  l-nrijdu  —  the  firsl  trace  of  the 
dental  follicle — originates  from  points 
upon  the  tree  extremity  of  this  lamina. 
They  show  themselves,  at  first,  as  slight 
tubercles  arranged  at  intervals  along  the 
margin  of  the  lamina,  and  corresponding, 
in  number  and  situation,  to  the  teeth  that 
will  be  developed  in  the  firsl  dentition. 
To  these  protuberances  we  give  the  name 
of  primitive  bowrgeon  of  the  follicle  (the 
first  follicular  budding,  or  bud). 

[In  a  foot-note  these  authors  give  their  theory  of  the 
origin  of  the  supernumerary  teeth;  but,  as  Dr.  Magitot  (the 
surviving  author  of  this  work)  has  since  modified  his  views 
in  relation  to  this  phenomenon,  a  mere  statement  of  the 
theory  advanced  by  them  will  here  be  sufficient.  Dra. 
Legros  and  Magitot  maintained  that  the  supernumerary 
teeth  originate  either  from  the  epithelial  lamina,  from 
supernumerary  buddings  arising  between  the  normal  num- 
ber; or  that  they  are  off-ahoots  from  the  epithelial  cord. 
In  the  Bra!  case  the  development  of  these  teeth  would  be 
precisely  Bimilar  to  that  of  the  deciduous  teeth;   in  the 


6Q  THE    ORIGIN    AND    FORMATION 

other,  to  that  of  the  permanent  teeth,  with  the  exception 
of  the  first  molar. 

The  present  views  of  Dr.  Magitot  upon  this  subject  (as 
recorded  on  pp.  36-7  of  his  treatise  on  the  Anomalies  of  the 
Teeth,  1877,)  are  in  accord  with  those  previously  advanced 
by  Kollmann;  and  are  based  upon  the  well-known  fact,, 
that  when  the  epithelial  cord  or  neck,  which  connects  the 
enamel-organ  with  the  epithelial  lamina,  becomes  severed 
by  the  closure  of  the  follicle,  the  cells,  of  which  the  cord  is 
composed,  multiply  to  a  greater  or  less  extent  at  their 
severed  extremities, — sometimes  in  great  abundance.  These 
epithelial  proliferations  sometimes  continue  adherent  to 
the  remains  of  the  cord,  and  to  the  follicle  itself,  until  they 
are  absorbed;  and  sometimes  considerable  masses  become 
detached,  and,  assuming  various  forms,  wander  into  the 
depths  of  the  jaws  (Fig.  19).  These  epithelial  proliferations,, 
according  to  Kollmann  and  Magitot,  may  become  the- 
enamel-germs  from  which  the  supernumerary  teeth  ori- 
ginate. 

Now,  in  order  that  a  tooth  may  be  produced,  a  super- 
numerary dentine-papilla  must  be  provided  for  this  ad- 
ventitious enamel-organ.  This  would  result  as  a  natural 
consequence,  if  the  theory  advanced  by  the  translator  of 
this  work  in  a  recent  Report  on  Dental  Physiology,  before 
the  American  Dental  Association,  is  correct.  (See  Trans. r 
1878,  pp.  56-57).  In  this  paper  it  was  maintained  that 
dentine-papilke  may  originate  from  any  point  of  the  den- 
tinal sheet  of  tissue  (as  described  by  Dursy),  with  which 
the  epithelial  mass  comes  in  contact;  that  it  is  solely 
through  the  influence  of  the  enamel-organ  upon  this  tissue, 
that  the  development  of  a  dentine-papilla  is  induced.     If 


OF   THE    DENT  \\.    FOLLICLE. 
Fig.  19. 


<;: 


'MB®' 


-        a      Ma^s«^H 


Fig.  19.— Taken  from  a  bovine  embryo,  magnified  100 
diametere.  Tbia  section  is  taken  after  the  rupture  of  the 
epithelial  cord,  and  shows  the  epithelial  proliferations  that 
occur  in  this  region  at  this  period  of  evolution.  The  cut 
represents  the  territory  between  the  wall  of  the  follicle  (o) 
and  the  mucous  membrane  (<l). 

//.  Epithelial  buddings  From  the  follicular  wall :  /■:.  /■:.  bud- 
dings and  debris  of  the  cord;  F.  globular  masses  from  the 
epithelial  lamina. 


68  THE    ORIGIN    AND    FORMATION 

this  be  true  the  origin  of  a  supernumerary  dentine-papilla 
is  readily  accounted  for;  while  otherwise,  special  papillae 
must  originate  independently,  and  coincidently  with  the 
supernumerary  enamel-organ, —  a  circumstance  that  does 
not  come  within  the  range  of  probabilities. 

Thus,  also,  it  seems  to  me.  we  find  a  rational  and  sat- 
isfactory explanation  of  the  origin  of  those  families  of 
dwarfed  teeth  found  in  dentigerous  cysts. — Tr.] 

This  bourgeon  retains  its  connection  with 
the  lamina,  from  which  it  is  a  direct  deriva- 
tion, by  means  of  a  slender  cord  or  neck, 
which  gradually  lengthens  as  the  terminal 
mass  increases  in  dimensions. 

During  the  whole  course  of*development 
this  bourgeon  constitutes  the  enamel-organ; 
while  the  neck,  in  its  progressive  lengthen- 
ing, only  serves  as  a  temporary  bond  uniting 
it  to  the  lamina. 

At  its  first  appearance  the  primitive 
bourgeon  presents  a  nearly  spherical  form 
(Fig.  20,  E),  and  is  comj^osed  of  an  external 
layer  of  prismatic  cells  (a  continuation  of 
those  of  the  lamina),  inclosing  a  mass  of 
polygonal    cells ;    the  latter  being  always 


OF   THE    DENTAL    I  <  LLICLE.  69 

Less  in  diameter  than   those  contained  in 
the  lamina 

Fig.  20. 


FlG.  '20.— A  section  of  the  epithelial  lamina  taken  from 
an  embryonic  lamb,  a  little  older  than  that  from  which  Fig. 
18  was  taken.     (Magnified  350  diameters.) 

c,  I  'rismatic  or  columnar  cells, —  a  continuation  of  the  low- 
est layer  of  the  Malpighian  stratum;  tf,  large  polygonal  cells 
of  the  epithelial  band  (Jbourrelet);  E,  smaller  cells  of  the 
epithelial  lamina.  This  lamina  presents  an  enlarged  ex- 
tremity, and  this  enlargement  represents  the  commencement 
of  the  enamel -organ. 

[The  prismatic  and  the  polygonal  cells  are  beautifully 
drawn  in  this  figure.] 

(§ee  advancing  stage  of  development,  fig.  31.) 

Let  us  here  add  thai  during  the  progress 
of  evolution  these  elements  (inclosed  in 
the  prismatic  investmenl  )  undergo  a  modi- 
fication  whereby  the}  are  transformed  into 
stellate  bodi< a  phenomenon  thai   never 


70  THE    ORIGIN    AND    FORMATION 

occurs  in  the  cells  of  the  cord  or  of  the 
lamina.  The  disparity  in  the  size  of  these 
cells,  together  with  the  morphological 
changes  they  experience,  seems  to  us  suffi- 
cient to  establish,  from  this  period,  a  very 

Fig.  21. 


Fig.  21. —  A  section  taken  from  the  lower  jaw  of  an 
ovine  embryo  (left  side),  measuring  72  millimetres.  (Mag- 
nified 80  diameters.) 

d,  E,  Same  as  in  the  preceding  figures,  g,  Commence- 
ment of  the  enamel-organ. 

clear  distinction  between  the  constitution 
of  the  lamina  and  that  of  the  bourgeon 
which  emanates  from  it.  We  would  em- 
phasize this  point,  from  the  fact  that  the 
more  recent  authors  that  have  written  upon 
this  subject  have  confounded  these  two 
parts  with  each  other. 


OF   THE    DENTAL    FOLLIOL]  .  71 

These  differences,  however,  will  be  more 
clearly  manifest  during  the  progress  of  evo- 
lution, when  we  shall  find  the  elements  of 
the  bourgeon  [enamel-organ]  undergoing 
a  -cries  of  important  changes;  whereas 
those  of  the  lamina  will  invariably  retain 
their  original  appearance. 

In  continuing  its  evolution,  the  primitive 
bourgeon,  which  was  at  first  spherical,  be- 
comes somewhat  cylindrical,  though  it  -till 
pursues  a  horizontal  course  until  it  has  be- 
come Qoticeably  lengthened,  when,  by  an 
abrupt  inflection,  it  takes  a  vertical  direc- 
tion, and  sinks  into  the  depth  of  the  jaw. 
Thus  extending  its  course,  the  cord  ac- 
quires a  length  which  varies  according  to 
the  species  of  animal,  besides  undergoing 
certain  secondary  inflections.  In  man,  as  also 
in  the  dog,  the  cord  always  remain-  short, 
and  in  the  solipeds  it  is  still  shorter.  In 
the  calf  and  in  the  land)  —  animals  that 
arc  particularly  favorable  for  these  studies 
—  it  describes  divers  undulations;   bu1  we 


72  THE    ORIGIN    AND    FORMATION 

have  never  observed  in  the  primitive  cord 
that  spiroid  arrangement  described  by  some 
authors,*  and  for  which,  as  we  shall  see, 
the  secondary  cord  (that  of  the  permanent 
teeth)  is  so  remarkable. 

These  differences  in  the  length  of  the 
primitive  cord  are  explained  by  the  disposi- 
tion of  the  special  parts ;  and  determined,  on 
the  one  hand,  by  the  species  of  animals,  in 
which  the  jaws  have  a  greater  or  less  ver- 
tical height ;  and  on  the  other  by  the  nature 
of  the  future  teeth.  One  readily  sees  how 
the  cord  of  the  follicle  of  a  permanent 
tooth  ought  to  be  longer  than  that  of  the 
temporary,  since  it  must  accommodate  itself 
to  the  longer  passage  it  must  make  from 
the  place  of  its  origin  to  its  terminus  be- 
neath the  follicle  of  the  temporary  tooth. 

The  primitive  cord,  in  the  course  of  its 
progress,  presents,  moreover,  some  peculiar- 
ities worthy  of  notice.  These  are  the  phe- 
nomena of  lateral  buddings,  which  give  rise 

*See  Kollmann,  loc.  cit.,  Taf.  XIV,  Fig.  2,  v. 


<)K    THE    DKNTAL    FOLLICLE. 


:; 


to  snmll  rounded  Qodules,  in  the  form  of 
varicosil  ies,  \\  hicb,  in  t  heir  arrangement,  re- 
semble an  irregular  chaplet.  (Fig-  "-'-•  ''•» 
These  lit  t  Le  masses  are  composed  exclusively 

FlG.  22. 


6>? 


FlG.  '22. —  Taken  from  a  section  of  the  lower  jaw  of  an 
ovine  embryo,  measuring  82  millim,  in  length.  (Mag 
2G0  diameters.)  c,  Oral  epithelium;  /'.  epithelial  cord  and 
the  •"  varicosities"  referred  to  in  the  text:  </.  enamel-organ; 
//.  dentine  bulb;  /,  follicular  wall  rising  from  the  base  of 
thelbulb;  K,  bourgeon  from  which  the  follicle  of  the  per- 
manent tootb  will  emanate. 
6 


74  THE    ORIGIN    AND    FORMATION 

of  small  polyhedral  cells,  analogous  to  those 
contained  in  the  cord  itself.* 

It  is  from  these  masses  that,  at  a  later 
period,  after  the  cord  is  ruptured,  those 
numerous  epithelial  prolongations  spring, 
which  will  be  considered  hereafter.  It  is 
hardly  necessary  to  say  that  we  do  not 
here  confound  the  buddings,  just  described, 
with  that  special  production  from  which  the 
cord  of  the  secondary  follicle  originates, — 
a  point  to  which  we  will  return  further  on.. 

After  the  cord  has  changed  its  course 
from  a  horizontal  to  a  vertical  direction, 
its  extremity,  which  has  already  become 
enlarged  and  club-shaped,  acquires  still 
Greater  dimensions.  This  results  from  the 
multiplication  of  the  polyhedral  cells  which 
compose  most  of  its  mass,  and  from  the 

*  [The  cells  referred  to  as  being  in  the  cord  are  not 
shown  in  the  figure.  Only  the  prismatic  layer,  which 
forms  the  outer  coat,  is  represented  here.  The  cord  may 
be  compared  to  a  tubular  gland,  the  walls  of  which  are 
composed  of  a  layer  of  prismatic  cells  (a  continuation  of  the 
stratum  Malpighii),  and  the  inclosed  contents,  of  small 
polygonal  cells.     Tr.J 


<>F    THE    DENTAL    FOLLICLE.  75 

prismatic  cells  thai  form  the  surrounding 
layer,  whose  numbers  increase  in  the  same 
proportion.  This  epithelial  body  thus 
occupying  the  deeper  tissue  of  the  jaw 
soon  assumes  a  somewhat  spherical. form ; 
the  superior  pole  corresponding  with  its 
point  of  connection  with  the  cord,  while 
the  inferior  pole  points  toward  the  bottom 
of  the  jaw,  inclining  more  or  less  toward 
the  lingual  side.  This  mass  represents  the 
enamel-organ  as  fully  developed.  Shortly 
afterward  the  inferior  pole  becomes  slightly 
compressed  toward  the  center  of  the  enamel- 
organ,  which  results  in  the  formation  of  a 
concavity  in  its  lower  or  deeper  extremity; 
and  the  mass  then  assumes  a  shape  re- 
sembling a  hood  or  cap,  but  still  retaining 
its  connection  with  the  cord. 

This  phenomenon  of  compression  coin- 
cides with  the  appearance  of  a  new  organ 
in  the  jaws,  th  dentine-bulb  [dentine- 
papilla].  This,  in  fact,  originates  ;,t  the 
inferior   pole  of  the   enamel-organ,    where 


76  THE    ORIGIN    AID    FORMATION 

the  compression  takes  place.  It  first  ap- 
pears as  an  opaque  point,  but  it  soon 
assumes  a  conical  form,  and  its  summit 
produces  and  occupies  the  corresponding 
depression  in  the  enamel-organ. 

This  reciprocal  adaptation  of  the  two 
organs,  which  takes  place  from  the  first 
appearance  of  the  dental  bulb,  continues 
throughout  all  their  subsequent  phases; 
the  enamel-organ  always  covering  the  bulb, 
and  exactly  fitting  its  contours,  whatever 
may  be  its  form,  or  the  form,  number  and 
disposition  of  the  divisions  it  may  present. 
No  connection  of  tissue,  however,  exists  be- 
tween the  two  organs  at  any  stage  of  de- 
velopment. Dissections  of  these  parts,  their 
maceration  in  coagulating  liquids,  as  well 
as  the  examination  of  sections,  all  establish 
this  fact  beyond  question.  This  simple  juxta- 
position of  the  surfaces  of  these  two  organs 
ceases,  however,  at  the  base  of  the  bulb, 
where  the  enamel-organ  turns  back  upon 
itself  with  a  rounded  border.     (Fig.  22.) 


OF    THE    DENTAL    FOLLICLE.  <7 

It'  we  now  examine  the  composition  "I 
ill,,  enamel-organ,  [al  the  period  of  develop- 
in,. ni  represented  in  Fig.  22,  saj  about  the 
fifteenth  week  of  the  human  embryo,  |  we 
find  that  the  primitive  elements  (the  polyg- 
onal cells  which  occupy  its  centra]  portion, 
and  ilif  prismatic  cortical  Layer,)  have  under* 
gone  notable  modifications.  We  discover, 
in  fact,  that  the  middle  region  of  this  organ 
is  occupied  by  some  elements  of  B,newform^ 
essentially  differing  in  appearance  from 
that  of  the  original  cells.  Thes<  are  stelldU 
bodies,  composed  of  a  central  nucleus,  sur- 

Fig.  28. 


Fig.  28.— Stellate  cells  of  the  enamel-organ.  (Dia- 
grammatic, from  Frey).  Thesi  cells  are  also  very  well 
sliuwn  in  the  preceding  figure. 


78  THE    ORIGIN    AND    FORMATION 

rounded  by  a  transparent  or  finely  granu- 
lated mass,  which  ramifies  and  inosculates 
with  the  neighboring  elements.  (Figs.  22-3.) 

These  star-shaped  bodies  occupy  at  first 
only  the  center  of  the  enamel-organ;  those 
near  the  periphery  preserving  their  origi- 
nal polygonal  form,  but  becoming  stellate  in 
proportion  as  the  dimensions  of  the  organ 
increase.  It  will  be  noticed,  however,  that 
the  anastomosing  processes  are  always  much 
longer  and  more  ramified,  as  the  cells  are 
situated  nearer  to  the  central  portion ;  while 
in  the  vicinity  of  the  periphery  it  is  some- 
what difficult  to  distinguish  these  processes, 
as  they  are  here  only  rudimentary.  The 
elements  thus  described  are  immersed  in 
a  translucid  amorphous  mass,  coagulable  in 
acids,  and  having  the  consistence  and  ap- 
j^earance  of  the  white  of  an  egg. 

These  starred  bodies  —  or  "  stellate  cells," 
as  they  are  usually  termed, —  are  formed 
directly  at  the  expense  of  the  polygonal 
elements    composing  the  internal  mass   of 


OF    III  1-    DENTAL    FOLLICLE.  79 

the  enamel-organ.  The  process  is  as  fol- 
lows: The  substance  mentioned  above  in- 
terposes itself  Little  by  little  between  these 
originally  small  polyhedral  cells,  and  thus 
their  walls  lose  their  mutual  contact,  excepl 
at  certain  points  where  they  -till  cohere. 
A.s  a  dired  resuli  of  this  phenomenon,  the 
primitive  polygonal  cells  exhibit  a  number 
of  depressions  extending  from  their  exterior 
Burface  toward  the  center,  giving  them  their 
stellate  appearance. 

From  this  transformation  the  primitive 
cells  would  become  entirely  insulated  by 
the  intervention  of  this  new  mucous  forma- 
tion, were  it  not  for  these  connecting  pro- 
cesses, which  give  to  this  organ,  a-  a  whole, 
it-  peculiar  reticulated  appearance,  and  t<> 
each  cell  its  stellate  form.  It  is  a  remark- 
able tact  that  no  line  of  juncture  can  be 
discovered  where  these  cells  are  connected 
with  each  other,  the  various  re-agents  failing 
to  disclose  the  leasl  trace  of  it,  so  effectually 
have  these  parts  been  cemented  together. 


80  THE    ORIGIN"    AND    FORMATION 

According  to  this  theory,  the  stellate  ar- 
rangement of  the  "pulp"  of  the  eaamel-organ 
(the  intimate  composition  of  which  we  do 
not  purpose  to  describe  in  this  memoir)  re- 
sults from  a  simple  modification  of  the  form 
of  the  primitive  polygonal  cells, —  a  change 
which  they  have  undergone  passively,  as 
it  were.  These  elements  of  the  enamel- 
organ,  notwithstanding  their  stellate  form, 
must  be  regarded,  therefore,  as  absolutely 
epithelial  in  their  nature.  The  mechanism 
of  this  transformation,  however,  differs  ma- 
terially from  that  given  by  Kolliker,*  and 
after  him  by  several  other  anatomists,  who 
contend  that  these  primitive  cells  might 
take  this,  stellate  form  spontaneously.  Our 
opinion,  however,  is  in  conformity  with 
that  of  Waldeyer,f  who  was  the  first  to 
properly  examine  and  describe  this  phe- 
nomenon;    though    Huxley,  %    at   a   much 

*  Human  Histology,  French  trans.,  1869,  p.  497. 
f  Untersuchungen    liber   die    Entwicklung  der   Ziihne, 
Zeitschr.  f.  rat.  rned.  1865. 

%  Quart.  Journal  of  Microscopical  Sc,  1854,  pp.  55-56. 


OF    Till".    DENTAL    FOLLICLE:  s  1 

earlier  day,  had  advanced  the  idea  (h\  po- 
thetically,  it  is  true,)  thai  the  enamel-organ 
had  an  epithelial  origin ;  but  be  did  not 
indicate  the  mode  wherebj  the  transforma- 
tion of  it-  elements  was  effected.* 

Now  as  to  the pi'ismaHc cells :  duringthe 

*  The  epithelial  nature  of  the  enamel-organ  had  not  till 
recently  been  accepted  in  France;  but  ita  elements  were 
described  as  stellate  Bbro-plastic  bodies  I  Robin  and  Magitot, 

loc.  cit.,  p.  60).  This  conclusion  was  based,  however,  solely 
upon  the  form  that  these  elements  present;  and  the  same 
argument  may  be  used  to  controvert  this  opinion.  It  is 
this:  that  in  the  enamel -organ  the  borders  of  these  cells, 
between  the  radiated  filaments  which  are  drawn  out  from 
their  periphery,  are  always  concave,  while  in  the  stellate 
fibroblastic  bodies  these  borders  present  plane  or  convex 
surfaces  alternating  with  those  that  are  concave. 

[The  student  must  not  infer  from  the  above  that 
Huxley  was  the  first  to  advance  the  idea  that  the  enamel 
was  of  epithelial  origin;  for  this  opinion  was  held  by 
physiologist  a  Long  before  his  day.  The  discovery  accred- 
ited to  Huxley  is  this:  that  the.  cells,  constituting  the 
internal  mass  of  the  enamel-organ  (the  reticular  portion 
Burrounded  by  the  stratum  of  prismatic  cells),  are  only 
metamorphosed  epithelial  cells.  Heretofore  bistologiBta 
believed  these  to  be  stellate  connective-tissue  cells:  but 
the  peripheral  layer  was  then,  as  it  is  dow,  admitted  to  be 
composed  of  epithelial  cells.     Tu.] 


82  THE    ORIGIN    AND    FORMATION 

early  stage  of  evolution,  we  have  found 
them  identical  in  character  and  in  dimen- 
sions on  all  parts  of  the  periphery ;  but  the 
moment  the  enamel-organ  assumes  a  new 
form,  produced  by  the  development  of  the 
bulb,  this  stratum  undergoes  some  impor- 
tant modifications.  At  this  period,  in  fact, 
the  cells  of  that  portion  of  the  cortical  layer, 
which  occivpy  the  concave  face  of  the  enamel- 
organ,  and  which  consequently  lie  in  con- 
tact with  the  dentinal  bulb,  begin  to  in- 
crease in  length ;  while  those  constituting 
the  convex  surface  of  this  organ  sensibly 
diminish  in  size.  This  difference  in  the  di- 
mensions of  the  cells  occupying  the. two 
segments  of  the  prismatic  stratum  or  corti- 
cal layer  manifests  itself  more  and  more 
during  the  progress  of  follicular  evolution ; 
and,  as  we  shall  see  hereafter,  the  external 
layer  ["  external  epithelium  of  the  enamel- 
organ  "  disappears  long  before  the  com- 
plete atrophy  of  the  enamel-pulp ;  while 
the  other  [the  "internal  epithelium"]  still 


OF    III  I'.    DENTAL    FOLLICLE. 


83 


remains  to  perform  the  importanl  functions 
assigned  to  it.  Qamely,  tin  formation  of  th 

i  mtnh  I. 

The  prismatic  cells  of  the  concave  face 
of  the  enamel-organ  [the,  enamel-cells,  or 
ameloblasts*]  offer  some  peculiar  character- 

*  [The  term  ameloblast  is  compounded  of  Amel  (from  the 
French  Bmail),  enamel;  and  blast  (from  the  Greek blastos), 
germ.    This  compound  word  has  recently  been  introduced 
into  our  nomenclature  by  Prof.  Eames,  of  St.  Louis;  and 
owing  to  its  euphony,  its  concise  and  definite  expression, 
and  its  general  relations  to  the  terms  osteoblast,  odontoblast 
and  others,  it  ought,  as  it  seems  to  me,  to  be  adopted  by  the 
dental  histologist.     It  will  certainly  facilitate  the  descrip- 
tion of  the  parts  to  which  it  is  applied,  and  obviate  the 
repetition  of  long  descriptive  phrases.     I  shall,  therefore, 
follow  the  lead  of  Dr.  Black,  and  whenever  it  seems  best 
shall  substitute  this  new  term  for  phrases  of  equivalent 
meaning  that  may  be  found  in  the  original.    The  amelo- 
blasts are  the  enamel-cells.    They  constitute  the  prismatic 
layer  of  Legros  and  Magitot;    the   internal  epithelium   of 
Kolliker;   and   the  adamantine  membrane  of   Raschkow; 
namely,  that  section  of  the  stratum  Malpighii  forming  the 
peripheral  layer  which  lines  the  concave  face  of  the  enamel- 
organ,  and  lies  i»  immediate  contact  with  the  dentine-bulb. 
The  other  section  of  this  stratum  covers,  or  rather  constitutes, 
the  convex  surface  of  the  enamel-organ,  and  is  generally 
known  as  the  external  epithelium.     It  has  probably  been 


84  THE    ORIGIN    AND    FORMATION 

istics,  to  whicli  we  will  now  call  your  at- 
tention. Originally  identical  with  those  of 
the  [lowest  layer  of  the]  Malpighian  stratum, 
from  which  they  are  directly  derived,  these 
cells,  besides  increasing  in  length,  expe- 
rience some  important  changes  in  form. 
The  extremity  that  is  directed  toward  the 
center  of  the  organ,  becomes  long  and  slen- 
der, forming  jjrocesses  which  unite  with  or 
are  continuous  with  the  filaments  that  pro- 
ceed from  those  neighboring  cells  which  con- 
stitute the  portion  of  the  enamel-organ 
known  as  the  stratum  intermedium*    The 

previously  noticed  that  the  peripheral  layer  has  been  divided 
into  two  sections.  This  has  been  done  simply  for  con- 
venience of  description,  there  being  no  anatomical  division 
between  these  two  portions ;  the  cells  being  alike  and  con- 
tiguous, although  at  a  later  period  they  experience  those 
dissimilar  modifications  that  are  fully  and  clearly  described 
in  the  text.     Tr.]  ' 

*  [As  this  portion  of  the  enamel-organ  is  only  inci- 
dentally mentioned  in  this  work,  a  few  words  of  explana- 
tion may  not  be  out  of  place  here.  It  might  with  pro- 
priety be  termed  the  stratum  of  Hannover  since  he  is  its 
accredited  discoverer..  This  "stratum  intermedium"  is 
not  represented  in  any  of  these  cuts,  but  it  consists  of  a 


OF   THE    DENTAL    FOLLICLE. 

opposite  or  peripheral  extremity,  thai  is 
bo  say,  the  bo8(  of  these  cells,  presents  the 
regular  prismatic  form  of  a  hexagon.  (Fig. 
24.)     It'  we  n<>\\   examine  an   underanged 


[Fig.  24  represents  the  basal  aspect  of  a  layer  of  amelo- 
blasts.    Tu.] 

layer  oftlic-c  prismatic  cells,  or  ameloblasts, 
magnified  about  400  diameters",  we  shall 
find  that  the  free  margin  of  this  layer  (that 
is  to  say,  the  part  that  corresponds  to  the 

few  layers  of  cells  that  still  retain  nearly  their  primitive 
form,  and  lies  between  the  layer  of  ameloblasts  and  the 
stellate  portion  of  the  "enamel-pulp."  Prof.  Tomes  (in 
his  Man.  of  Dental  Anat.,  p.  125)  describes  it  thus:  "The 
'stratum  intermedium'  consists  of  cells  intermediate  in 
character  between  those  of  the  bordering  epithelium  and 
the  stellate  reticulum;  they  are  branched,  bat  less  con- 
spicuously so  than  the  stellate  cells,  with  which  on  the 
one  hand  they  are  continuous,  on  the  other  with  the 
enamel    cells."      The    special    functions  of   these  cells    is 


86  THE    ORIGIN    AND    FORMATION 

base  of  these  cells )  appears  clearer  than 
the  bodies  of  the  cells  themselves,  and  in 
fresh  preparations  seems  like  a  continuous 
line.  If,  however,  a  like  examination  be 
made  of  some  hardened  preparations,  or  if 
careful  means  be  taken  to  detach  this  mar- 
ginal line,  which  the  edge  of  a  section  of  the 
plateau  represents,  from  the  base  of  the 
cells,  it  will  be  found  that  it  can  be  sub- 
divided into  as  many  sections  as  there 
are  cells  in  the  layer.  And  yet  some  prep- 
arations may  be  met  with,  in  which  more 
or  less  of  this  clearer  line  becomes  detached 
in  the  form  of  a  shred  'of  ribbon.  It  is  this 
strip,  which  is  evidently  made  continuous 

questionable.  Waldeyer  believes  that,  since  "the  enamel 
cells  may  be  frequently  seen  to  be  connected  at  their 
lower  extremities  with  the  cells  of  the  stratum  interme- 
dium, a  multiplication  of  the  enamel- cells  from  the  cells 
of  this  stratum  in  the  direction  of  their  length  may  be 
admitted  to  occur  "  (Strieker's  Hist.,  p.  334);  an  opinion 
shared  by  Hertz  and  the  author  first  quoted,  but  differing 
from  that  of  Magitot  and  Kolliker.  A  further  description 
of  these  cells  would  more  properly  come  under  the  head 
of  Development  of  the  Enamel.     Tr.] 


OF    THE    DENTAL    FOLLICLE.  87 

1>\  artificial  means,  thai  ha-  given  rise  fco 
the  hypothesis  fchal  a  membrane  invests  or 
lines  the  concave  face  of  this  stratum  of 
cells,  ameloblasts.  AW-  shall  sec,  moreover, 
in  examining  these  peculiarities  in  detail, 
thai  this  appearance  is  not  specially  and  ex- 
clusively confined  to  the  cells  of  i  he  enamel- 
organ,  since  it  exists  wherever  we  find  the 
prismatic  cells  provided  with  what  lias  been 
termed  a  'plateau.  The  prismatic  cells  of 
the  intestines  are  known  to  be  thus  sup- 
plied. Now  it  happens,  that,  whether  this 
plateau  remains  adherent  to  each  c<ll  s,j><i- 
rateh/j  or  whether  it  becomes  adherent  to 
those  of  the  neighboring  cells,  so  that  a 
strip  may  be  detached  presenting  the  ap- 
pearance of  a  true  membrane,  depends  en- 
tirely upon  the  mode  of  treatment  to  which 
the  preparation  is  subjected. 

I'k  \.\k  :  This,  I  inter,  is  the  basement,  or  pre- 
formative,  membrane  ( 

Teacher:  The  edge  of  the  tissue  that  forms, 
in  section/ the  clear  line,  is  not  the  same  Btruc- 


88  THE    OBIGIN    AND    FORMATION 

tnre  described  (p.  17)  as  the  membrana  prce- 
formativa  of  Haschkow ;  the  membrane  here 
discussed  is  situated  between  the  latter  tissue 
and  the  layer  of  ameloblasts ;  and  these  two 
structures,  thus  lying  in  apposition  with  each 
other,  correspond  with  the  "  double  pellucid 
layer"  mentioned  by  Dr.  Black,  in  his  report 
on  Histology  (p.  72  Trans.  A.  D.  A.,  1878), 
in  which  he  says:  "  Just  before  the  calcifi- 
cation, and  even  before  the  odontoblasts  make 
their  appearance,  the  ameloblasts,  and  the  tis- 
sues of  the  pulp,  are  separated  by  a  well  marked 
double  pellucid  layer ;  which,  in  section,  appears 
as  a  double  band,"  etc.  The  two  white  parallel 
lines  A,  A,  fig.  25,  represent  this  "double  band  "; 
the  upper  one  being  the  tissue  here  described 
by  our  authors,  and  which  is  identical  with  the 
membrana  prwfomnativa  of  Huxley  ;  while  the 
lower  one  represents  the  basement  membrane  of 
Todd  and  Bowmann,  and  the  membrana  prce- 
formativa  of  Raschkow.  The  clear  line  referred 
to  in  the  text  as  being  seen  at  the  edge  of  a 
section  of  a  layer  of  enamel-cells, —  namely,  the 
upper  line  of  the  double  pellucid  zone,  or  the 
preformative  membrane  of  Huxley, —  is  formed 
by  the  artificial  union  of  the  opercula  that  cover 
the  dentinal  extremities  of  the  ameloblasts. 


OF   THE    DENTAL    FOLLICLE.  B9 

The  figure  below  is  an  ideal  representation  of 
a  dental  follicle  before  it  lias  lost  its  connection 
with  the  epidermis.  The  object  of  this  cut  is 
to  show  the  relation  of  the  basement  membrane 
and  the  two  different  structures  (one  of  which  is 

Fig.  25. 


A.    A. 


Fig.  25. — B  M,  basement  membrane;  X,  neck;  S,  sac  or 
follicular  wall;  0,  enamel -organ;  B,  bulb;  E  E,  external 
epithelium  of  the  enamel-organ  and  the  basement  mem- 
Inane:  /•;  ('.  epithelial  cord;  C  T,  connective  tissue  sur- 
rounding the  enamel-organ;  Ep,  epidermis  or  oral  epithe- 
lium. 

The  parts  embraced  between  the  points  where  the  di- 
vergent lines  A  A  terminate,  are:  — (1)  the  concave  face  of 
the  enamel-organ,  lined  with  a  layer  of  ameloblasts,  or  the 
"internal  epithelium":  (2i  the  membrana  pra-formativa  of 
Huxley,  or  the  tissue  compos.. 1  of  the  basal  coverings  of  the 
ameloblasts;  (3)  the  membrana  prseformativa  of  Raschkow, 
or  the  basement  membrane;  (4)  the  dentine-bulb  itself. 
I  diagrammatic. 
7 


90  THE    ORIGIN    AND    FORMATION 

known  as  the  membrana  prseformativa  of  Rasch- 
kow,  and  the  other  as  that  of  Huxley)  to  the 
adjacent  parts.  The  white  line  terminating  on 
either  side  of  the  upper  portion  of  the  figure 
represents  the  basement  membrane,  and  sepa- 
rates the  epidermal  from  the  dermal  tissues.  The 
mass  embraced  within  the  walls  of  this  devious 
line  is  composed  of  epithelial  cells ;  that  found 
on  the  other  side  of  this  line  belongs  to  the 
dermal  tissue.  Now,  that  portion  of  the  mem- 
brane represented  by  this  line,  which  passes  be- 
tween the  enamel-organ  (O)  and  the  dentine-bulb 
(B),  and  which  constitutes  the  peripheral  layer 
of  the  latter  (A  A),  is  said  to  assume  important 
functions  in  the  development  of  the  dentine;  and 
hence  was  denominated  the  membrana  prseforma- 
tiva  by  Raschkow;  a  name  it  still  retains,  although, 
as  to  its  nature  and  office,  physiologists  are  not 
agreed.  The  upper  line  running  parallel  to  this 
membrana  pneformativa  of  Raschkow,  as  before 
stated,  represents  the  membrana  prseformativa  of 
Huxley ;  and  by  him,  Schwann,  Kolliker,  Magi- 
tot,  and  some  others,  special  functions  have  been 
assigned  to  it  in  the  formation  of  the  enamel. 
But  you  must  not  infer  from  what  has  been  said 
that  the  last  named  authors  precisely  agree  as  to 


OF    THE    DENTAL    FOLLICLE.  9] 

the  nature  of  this  membrane,  or  as  to  the  mode 
of  enamel-development,  amelification. 

Caspeb:  This  term  membrana  prcBformativa 

is  about  as  equivocal  as  that  of  mucous  mem- 
brane, for  I  have  already  found  it  applied  to 
three  different  tissues,  one  of  which  is  said  to 
line  the  walls  of  the  pulp-chamber. 

Teacher:  The  latter  consists  of  a  layer  of 
odontoblasts,  and  is  generally  called  the  mem- 
brana eboris.  But  we  must  discontinue  for  the 
present  the  discussion  of  these  tissues,  the  nature 
and  functions  of  which  (and  even  the  existence 
of  some  of  them)  are  still  matters  of  dispute. 
Nevertheless,  these  histological  tacts  or  appear- 
ances will  be  found  useful  hereafter  in  studying 
the  development  of  the  enamel  and  dentine. 

As  to  the  nucleus  of  the  prismatic  cells 
[the  cmieloblasts]  of  the  enamel-organ,  we 
find  that  its  position  varies  in  relation  to 
the  ends  of  the  cell,  according  to  the  period 
of  development;  at  first  it  is  aboul  equi- 
distant, bu1  it  afterward  appears  to  move 
toward  the  tapering  extremity.  This  ap- 
parent ehano-e  of  place,  however,  ta  no1  real. 


92     -       THE    ORIGIN    AND    FORMATION 

but  results  from  the  more  rapid  growth  of 
the  dentinal  end  of  the  cell  (which  is  re- 
markably active  after  the  development  of 
the  bulb),  thus  causing  the  nucleus  appar- 
ently to  move  away  from  it.  This  differ- 
ence in  the  development  of  the  extremities 
of  the  ameloblasts  is  especially  remarkable 
in  the  enamel-organ  of  the  incisors  of  the 
rodents,  in  which  these  elements  attain  to 
great  length. 


OP    'NIK    DENTAL    FOLLICLE,  '.»."> 


CHAPTER  III. 


ORIGIN  AND  FORMATION  OF  THE  DENTAL  BULB.  AND  OF 
THE  FOLLICULAR  WALL. 

AS  we  have  just  seen,  the  enamel-organ 
-*--*-  sooii  loses  its  spherical  form  and 
acquires  the  appearance  of  a  hood  or  cap; 
and  this  change  in  form  is  contemporaneous 
with  the  appearance  of  a  new  component 
part  of  the  follicle, — the  dentinal  bulb.  A 
alight  opacity  appears  on  the  point  of  em- 
bryonic tissue  of  the  jaw,  that  corresponds 
to  tlif  depression  in  the  enamel-organ. 
This  opacity  is  due  to  the  production  of 
new  elements,  which  are  grouped  in  such  a 
manner  as  to  form  at  first  a  Little  rounded 
nipple  of  hemispheric  form,  the  convexity 
of  which  corresponds  exactly   to   the   de- 


94  THE    ORIGIN    AJSTD    FORMATION 


pression  or  concavity  of  the  enamel-organ. 
(Fig.  26,  H.) 


FIG.  26. 


Fig.  26. — Vertical  section  taken  from  the  incisive  region  of 
the  lower  jaw  of  an  ovine  embryo,  measuring  115  millimeters, 
magnified  80  diameters,  a,  Meckel's  cartilage;  b,  osseous 
formation;  c,  section  of  the  dental  artery;  d,  epithelial 
band  (bourrelet);  E,  epithelial  lamina;  F,  cord;  g,  enamel- 
organ.     Meckel's  cartilage  at  the  right  of  the  cut. 

H  represents  the  incipient  dental  bulb.  The  drawing 
for  this  cut  preserves  the  defects  in  the  specimen  from  which 
it  was  taken.  For  example:  the  space  between  the  enamel- 
organ  and  the  follicular  wall  is  caused  by  the  shrinkage  of 
the  former, —  a  result  of  too  long  maceration  of  the  parts. 
Similar  defects  will  be  found  in  several  of  the  following 
cuts. 


OF    THE    DENTAL    FOLLICLE.  '.».> 

This  little  papilla,  which  represents  the 
incipienl  dental  bulb,  is  composed  a1  firsi 
only  of  nucleated  embryoplastic  elements, 
and  soon  afterward  of  fusiform  and  Btellate 
bodies.  It  will  be  noticed,  also,  that  at 
this  early  stage  of  development  a  vascular 
loop  enter-  it-  substance,  similar  to  those 
Pound  in  the  papillae  of  the  skin;  but  we 
have  not  been  able  to  discover  in  it  any" 
nerve-fibres  until  it  has  attained  a  mam- 
millated  form.  The  l>ull>  retains  this  latter 
form  but  a  brief  period,  for  it  soon  shows 
a  tendency  to  take  that  of  the  future  tooth: 
thus,  for  the  incisors  and  canines,  it  assumes 
a  conical  form;  for  the  molars,  in  man  and 
the  carnivora,  the  primitive  papilla  i>  soon 
covered  with  secondary  protuberances,  equal 
in  number  to  tin-  cusps  of  tin  future  crown  : 
and  in  the  compound  molars  of  the  herbiv- 
ora  and  rodents  throws  out  prolongations 
which  represent  also  the  future  divisions  of 
the  crown.  An  analogous  arrangemenl  is 
found  in  the  incisors  (d  corne£)  of  the  soliped. 


96  THE    ORIGIN    AND    FORMATION 

Iii  all  these  circumstances  the  enamel- 
organ  allows  itself,  as  it  were,  to  be  moulded 
by  the  bulb,  so  as  to  exactly  conform  to 
whatever  configuration  the  latter  may  as- 
sume. 

Casper  :  The  dentine-papilla  determines,  then, 
the  form  or  contour  of  the  crown  of  the  future 
tooth  ?  I  inferred  from  a  remark  you  made  (in 
regard  to  the  supernumerary  teeth,  I  think,) 
that  it  was  the  enamel-organ  that  controls  this 
matter ;    at  least,  that  this  was  your  opinion. 

Teachee  :  Whatever  views  I  may  entertain 
as  to  the  influence  exerted  by  the  enamel-organ 
have  been  mainly  derived  from  these  authors, 
though  I  have  recently  given  this  subject  con- 
siderable thought.  This  is  one  of  the  points  in 
dental  physiology  that  has  been  almost  entirely 
ignored  by  authors  who  have  written  upon  the 
development  of  the  teeth.  Drs.  Legros  and 
Magitot,  however,  express  very  decided  views 
in  regard  to  it,  though  they  do  not  state  the 
reasons  upon  which  their  opinion  is  founded. 
In  a  more  recent  work  (Traite  des  Anomalies, 
etc.,  Paris,  1877,)  Dr.  Magitot,  the  surviving 
author  of  the  present  treatise,  maintains,  very 


<>K    THE    DENTAL    1  OLLH  I.K.  97 

positively,  that  the  enamel-organ  is  endowed  with 
this  influence.     These  are  his  words: 

••  It  is  explicitly  admitted  that  the  epithelial 
cord,  or  enamel-organ,  dominates  and  determines 
the  place  and  the  form  of  the  tooth.  The  gene- 
sis and  development  of  the  dental  bulb  (dentine- 
germ),  which  makes  its  appearance  subsequently 
to  the  cord,  is  absolutely  dependent,  as  a  physio- 
logical consequence,  upon  the  presence  and  fo?'m 
of  the  enamel-organ  itself.  One  will,  neverthe- 
less, be  tempted  to  believe,"  he  continues,  "  that 
the  nature  of  the  future  tooth  is  under  the  control 
of  the  dentine-papilla,  a  kind  of  organic  mould 
upon  which  the  calcific  elements  are  grouped ; 
but  it  must  be  remembered  that  the  epithelial 
cord,  which  represents  the  future  enamel-organ, 
always  precedes  the  appearance  of  the  dentine- 
papilla,  which  never  originates  till  the  cord  has 
advanced  a  certain  distance  in  its  course.  Accord- 
ingly, we  believe  that  the  epithelial  cord  decides 
Dot  only  the  place  of  genesis,  but  the  form  and 
function  of  the  corresponding  tooth." 

It  will  be  seen  from  the  above  quotation  that 
I>r.  Magitot  dissents  from  the  general  opinion  in 
regard  to  the  influence  which  these  parts  i  namely, 
the  enamel-organ  and  the  dentine-germ)  exercise 
upon  each  other. 

AlB  for  myself,  I  had  supposed  that  the  enamel- 


98  THE    ORIGIN    AND    FORMATION 

organ  was  the  more  passive  structure,  and  that 
its  form,  at  least,  was  determined  by  the  dentine- 
'  papilla.  But,  in  considering  this  subject  more  care- 
fully, and  examining  both  sides  of  the  question, 
I  discover  evidence  which  strongly  confirms  the 
theory  of  Dr.  Magi  tot.  My  conclusions  rest 
mainly  upon  a  certain  fact  in  the  statement  of 
Dursy,  who,  according  to  Waldeyer,  says : 

"  The  first  germ  of  dentine  appears  in  the  den- 
tal saculus,  as  a  dark,  semi-lunar  area  at  the  bot-  - 
torn  of  the  dental  groove, —  that  is  to  say,  of  the 
enamel-germ,  —  coetaneously  and  continuously 
with  which  it  is  developed  along  each  half  of  the 
jaw.  At  certain  points,  corresponding  to  the 
position  of  the  subsequent  teeth,  the  young  struct- 
ure develops  in  the  form  of  papillae,  projecting 
against  the  enamel-germs,  while  the  remainder 
atrophies.  The  two  horns  of  the  semi-lunar  mass 
(as  seen  in  section)  extend  from  the  base  of  the 
dental  papilla  some  distance  upward,  and  em- 
brace the  dentine-germ  and  enamel-organ."  • 

The  particular  point  in  this  statement  of  Dursy 
to  which  I  allude,  and  to  which  I  wish  to  call 
your  special  attention,  is  that  referring  to  the  semi- 
lunar area  of  tissue  extending  along  each  half  of 
the  jaw,  and  from  which  the  dentine-germs  are  de- 
veloped.   If  the  anatomical  description  of  Dnrsy 


OF   THE    DENTAL    FOLLICLE.  '•,'•, 

is  correct  (ami  lam  not  aware  thai  it  is  disputed), 
a  dentine-germ  might  be  developed  from  any  poinl 
of  this  semi-lunar  area  which  should  be  reached 
by  the  enamel-organ.     No  particular  point  is 

assigned  to  the  development  of  any  especial  den- 
tine-germ :  that  is  entirely  accidental,  and  de- 
pends upon  the  course  which  the  enamel-organ 
takes. 

For  example :  It"  the  epithelial  cord  of  a  cuspid 
should  deviate  from  its  normal  course,  so  as  to 
come  in  contact  with  this  dentinal  sheet  of  tissue 
at  a  point  between  the  bicuspids,  the  cuspid 
would  be  developed  between  those  two  teeth.  In 
fact,  whatever  point  in  this  tissue  the  enamel- 
organ  of  the  cuspid  should  reach,  the  future 
tooth  would  be  a  true  cuspid. 

If  this  be  admitted,  the  theory  of  Dr.  Magitot 
must  be  true, — that  the  enamel-organ  determines 
the  form  and  character  of  the  future  tooth. 

If  the  fact  that  the  teeth  of  certain  fishes  are 
wholly  destitute  of  -enamel,  seems  to  militate 
against  this  theory,  we  have  the  statement  from 
high  authority  that  all  teeth,  whether  clothed 
with  enamel  or  not,  are,  in  the  formative  stage, 
universally  endowed  with  enamel-organs.  May 
we  not  infer,  then,  that  in  such  cases  the  rudi- 


100  THE    ORIGIN    AND    FORMATION 

mentary  enamel-organ  has  performed  its  func- 
tions when  it  has  incited  the  development  of  the 
dentine-germ,  and  determined  ito  future  form 
and  character?* 

As  the  dental  bulb  develops  in  height, 
it  takes  a  slightly  oblique  direction  in  re- 
lation to  the  axis  of  the  follicle,  and  at  the 
same  time  undergoes  a  certain  constriction 
at  its  base,  thus  forming  a  kind  of  neck 
at  the  line  where  (as  has  been  already 
seen)  the  enamel-organ  is  reflected  back 
upon  itself.     (Fig.  27.) 

There  is,  however,  one  .peculiarity  in  the 
structure  of  the  bulb  which  we  ought  par- 
ticularly to  notice  here,  and  that  is  the  na- 
ture of  the  external  surface  of  this  organ. 

If  you  examine  the  structure  of  a  vertical 
section  of  the  bulb,  you  will  find  that  there 
exists  at  the  periphery  of  this  organ  a  thin, 
clear  zone,  which  is  easily  distinguished 
from  the  subjacent  tissue  by  its  refraction. 

*  [Extract  from  my  report  on  Dental  Physiology,  read 
before  the  American  Dental  Association,  August,  1878. — Tit.] 


OF    THE    DENTAL    FOLLICLE.  1<»1 

This  zone  to  which  several  anatomists  have 
assigned  important  functions,  is  only  a  thin 
stratum  of  amorphous  material,  which  is 
wholly  destitute  of  anatomical  elements  and 
of  granulations. 

This  amorphous  layer  is  not  only  more 
Transparent,  but  somewhat  denser,  than  the 
subjacent  tissue  of  the  bulb,  so  that  some- 
times it  may  be  detached  from  the  surface  of 
the  latter.  This  fact  has  led  many  anat<  >mists 
to  suppose  that  the  bulb  was  invested  with 
a  distinct  membrane  (the  memhrana  pivfor- 
mativa  of  Raschkow).  (Fig.  25,  lower 
parallel  line,  A  A,  p.  89.) 

We  shall  describe,  in  another  work,  the 
nature  and  functions  of  this  structureless 
layer,  but  we  will  say  this  much  in  advance, 
that  it  is  in  this  tissue  that  the  ivory-cells 
[odontoblasts  |  make  their  first  appearance. 

As  soon  as  this  little  mass  of  new  ele- 
ments, which  constitutes  the  dental  bulb, 
has  taken  a  hemispheric  form,  two  opaque 
processes,  originating  at  its  base,  ascend  di- 


102  THE    OKIGIN    AND    FORMATION 

vergently  upon  its  sides;  these  appear  to 
emanate  directly  from  the  tissues  of  the  bulb 
itself,  and  they  represent  the  first  trace 
.of  the  wall  [sac]  of  the  future  follicle. 
(Fig  22  I,  p.  73.) 

If,  at  this  period,  the  constitution  of  these 
follicular  processes  be  studied,  we  find  them 
composed  of  exactly  the  same  elements  as 
the  bulb  from  which  they  originate.  As 
the  bulb  continues  to  develop,  these  pro- 
cesses also  increase  in  length,  and  bend 
round  toward  each  other,  in  such  a  way  as 
to  finally  embrace  in  their  double  concavity 
not  only  the  bulb  itself  but  also  the  enamel- 
organ,  which,  as  you  already  know,  constant- 
ly crowns  the  latter.  In  this  manner  the 
follicular  wall,  which  was  at  first  only  a 
little  collar  attached  to  the  neck  of  the  bulb, 
by  its  gradual  upward  growth  finally  em- 
braces and  isolates  both  the  enamel-organ 
and  the  dentinal  bulb. 

Caspee  :  We  are  told,  at  first,  that  the  fol- 
licular wall   originates  from    two   processes,   on 


OF    THE    DENTAL    FOLLICLE.  1 1 >3 

opposite  sides  of  the  bulb;  but  now  it  is  de- 
scribed as  a  little  colla/r  fixed  to  the  neck  of 
the  bulb  —  apparently   quite  another  thing. 

Teacher:  These  authors,  doubtless,  at  first 
describe  the  follicular  wall  as  it  appears  in  sec- 
tion. In  reality  it  must  be  a  circular  process, 
which,  in  the  diagrammatic  figure,  presents  the 
appearance  of  two.  Prof.  Tomes  says,  in  his 
Dental  Anatomy :  "From  the  base  of  the  den- 
tine-bulb prolongations  pass  outward  and  slight- 
ly upward,  so  that  they  in  a  measure  embrace 
the  free  edge  of  the  enamel-organ  ;  and,  at  a 
somewhat  later  period,  they  grow  upward  till 
they  fairly  embrace  the  whole  enamel-organ." 

Owen,  in  his  Odontography,  uses  the  follow- 
ing language:  "By  the  development  of  three 
or  four  lamellar  processes  from  the  opposite  sides 
of  the  mouth  of  the  follicle,  and  their  mutual 
cohesion,  the  papilla  is  inclosed   in  a  capsule." 

Prof.  "\Vedl,  in  his  Pathology  of  the  Teeth, 
says:  "The  dentinal  germ  proceeds  from  the 
floor  of  the  dental  sac  which  invests  it  and  the 
enamel-organ." 

K. illiker  (fifth  edition)  says:  "The  dentine- 
papilla  arises  from  the  bottom  of  the  dental  sac." 

Although  the  last  two  authors  do  not  minutely 


104  THE    ORIGIN    AND    FORMATION 

describe  the  process  of  development,  they  evi- 
dently do  not  mean  that  the  bulb  arises  from  the 
"bottom"  or  "floor"  of  a  formed  sac,  but  upon 
the  surface  of  a  sheet  of  tissue  which  finally 
forms  the  sac.  They  agree  with  Tomes  and  the 
authors  of  this  work,  excepting  that  the  former 
histologists  believe  that  the  base  of  the  dentinal 
bulb  is  inclosed  within  the  walls  of  the  sac; 
whereas  the  others  believe  the  follicle,  from  its 
apex  to  the  base  of  the  bulb,  to  be  invested  by 
the  sac. 

At  this  period  the  follicular  wall  may  be 
compared  to  a  muff  inflated  in  the  middle, 
the  lower  opening  of  which  corresponds  to 
the  base,  or  neck,  of  the  bulb  to  which  it  is 
attached ;  while  the  opposite  opening  corre- 
sponds to  the  neck  of  the  enamel-organ, 
that  is  to  say,  to  the  point  where  the  latter 
is  connected  with  the  epithelial  cord.  Soon 
afterward  the  cord  becomes  severed  at  this 
point,  by  the  resorption  of  its  constituent 
elements;  a  cessation  of  continuity  due, 
without  doubt,  to  the  compression  or  stran- 
gulation it  undergoes  from  the  encroaching 


OF    Till'.    DENTAL    FOLLICLE.  LOS 

walls,  which  u<>\\  unite  a1  this  poinl  and 
completely  inclose  the  follicle.  Thus  fclie 
enamel-organ  Loses  the  connection  which  it 
had  hitherto  maintained  with  the  epithelial 
lamina,  and  the  dental  follicle  may  be  re- 
garded as  definitely  completed.     (Fig.  27.) 

Fie.  87. 


— 4C 


Fig.  27. —  Section  of  the  lower  jaw  of  a  bovine  embi^o, 
magnified  80  diameters;  showing  the  dental  follicle,  as 
completed,  ami  the  surrounding  tissues. 

a.  Meckel's  cartilage;  /<.  traces  of  ossification;  r.  Lowes! 
8 


106  THE    ORIGIN    AND    FORMATION 

This  wall  [sac],  composed  primarily,  as 
we  have  seen,  of  embryoplastic  elements, 
gradually  assumes  the  aspect  of  a  distinct 
laminated  membrane,  which  may  be  sep- 
arated from  the  adjacent  tissues,  except  at 
the  base  of  the  bulb,  to  which  it  remains 
fixed. 

Kolliker,  with  most  other  authors,  de- 
scribes this  wall  as  composed  of  two  con- 
centric laminge ;  and  yet  admits,  with  Hux- 
ley, that  the  transparent  stratum  which 
clothes  the  bulb  (membrana  prceformativci) 
reflects  itself  back  on  its  internal  face,  and 
thus  lines  the  whole  inner  surface  of  the 
follicular  wall. 

We  will  reserve,  for  a  forthcoming  work, 
the  study  of  these  different  peculiarities  of 
structure. 

layer  of  the  Malpighian  stratum;  d,  oral  epithelium;  F, 
ameloblastic  layer;  lower  F,  external  layer  of  the  enamel- 
organ, — a  continuation  of  the  internal  layer  of  ameloblasts; 
g,  stellate  recticulum  of  the  enamel-organ;  H,  dental  bulb; 
I,  follicular  wall  (indistinct);  K,  buddings  of  the  cord. 
The  vascular  appearance  of  the  bulb  does  not  appear  in  the 
original. 


OF    i  in:    D]  xi  \i.    i  in. i. n  i.i:.  1«>7 

I'uwk:  With  my  ideas  of  the  parts  constitut- 
ing the  follicle,  I  fail  to  comprehend  how  the  pre- 
formative  membrane  can  line  the  internal  Burface 
of  the  follicular  wall  and  also  clothe  the  bulb. 

Teacher:  Perhaps  Kolliker's  definition  of 
the  follicle,  assisted  by  Fig.  2."),  may  enable  you 
to  better  understand  this  matter;  and  since 
it  is  brief,  1  will  give  you  the  benefit  of  it. 
In  his  "'tli  edition  it  reads  as  follows:  "The 
dental  sacs  [follicles]  are  composed  of  three 
parts, —  the  sac  properly  so-catted,  the  dental 
germ,  and  the  enamel-organ.  The  proper  dental 
sac  is  an  envelope  consisting  of  two  layers. —  an 
external  one  composed  of  dense  connective  tissue, 
ami  a  softer  internal  one,  of  a  gelatinous  consi 
ence,  containing  numerous  connective-tissue  cor- 
puscles, and  also  some  true  fasciculi  of  connective 
tissue.  This  internal  layer  is  limited  on  its  in- 
ner surface,  toward  the  enamel-organ,  by  a  homo- 
geneous layer  of  extreme  tenuity,  the  preform- 
ative  membrane  of  the  dental-germ'"  [bulb]. 

At  tin-  period  of  evolution  to  which  we 
have  arrived  in  our  description,  the  follicle 
i-  completed  and  closed,  tf  now  we  exam- 
ine it-  general  constitution,  we  shall  find  it 


108  THE    ORIGIN    AND    FORMATION 

composed,  proceeding  from  the  outside  in- 
ward — 

1st.  Of  the  follicular  wall  which,  clothes 
its  entire  surface, — except  the  base  of  the 
bulb,  which  remains  free.     (Fig.  27,  I.) 

2d.  Of  the  enamel-organ,  subjacent  to 
the  follicular  wall,  to  which  it  conforms  in 
its  whole  extent,  in  such  a  way  that  while 
its  external  face  corresponds  to  this  wall, 
its  lower,  concave  face  is  in  immediate  con- 
tact with  the  bulb.     (Gr.) 

3d.  Lastly,  of  the  hull  itself,  which  oc- 
cupies the  lower  and  central  portion  of  the 
follicular  sac.     (H.) 

Except  the  three  fundamental  parts  just 
named,  no  other  substance  finds  place  in 
the  constitution  of  the  follicle.  The  enamel- 
organ  exactly  fills  all  the  space  compre- 
hended between  the  wall  [sac]  and  the 
bulb,  and  terminates  at  the  base  of  the  lat- 
ter in  a  rounded  margin,  which  forms  the 
dividing  line  between  the  prismatic  cells 
that  clothe  both  its  concave   and    convex 


OF   THE    DENTAL    FOLLICLE.  L09 

surfaces  |  Sec  Fig.  25,  A  A  |.  This  bound- 
ary, however,  is  nol  artificial.  It  results, 
on  the  one  hand,  from  anatomical  differ- 
ences that  these  parts  now  present,  and, 
on  the  other,  from  the  physiological  role 
which  the  cells  of  the  concave  face  are 
called  upon  to  perforin:  whereas  the  exter- 
nal layer  atrophies  rapidly  and  disappears.* 
This  prismatic  layer  of  the  concave  surface 
(adamantine  membrane),  constituting,  as  we 
shall  see,  the  stratum  of  enamel-cells  |  amel- 
oblasts],  remains  a  long  time  in  the  compo- 
sition of  the  follicle ;  not  only  after  the  ex- 
ternal layer  has  disappeared,  but  even  after 
the  atrophy  of  the  gelatinous  part  of  the 

*  I  Waldeyer  and  Hertz  believe  this  external  layer  of  the 
enamel- organ,  instead  of  being  absorbed,  to  finally  become 
the  cuticula  dentis,  "  Nasniyth's  membrane."  Tomes,  Magi- 
tot  and  Wedl,  however,  attribute  this  membrane  to  another 
source,  believing  its  origin  identical  to  that  of  the  cement; 
while  Huxley  maintains  that  the  preformative  membrane 
(see  upper  line,  A  A.  Pig.  85),  after  the  enamel  is  completed, 
constitutes  this  thin  enamel  covering.  Though  Kolliker 
does  not  assent  to  the  latter  theory,  yet  he  believes  this 
membrane  to  be  a  product  of  the  enamel-organ. — Tb.  | 


110  THE    ORIGIN"    AND    FORMATION 

enamel-organ.  Let  us  farther  add,  that  in 
the  rodents  (whose  incisors,  as  we  know,  are 
of  continuous  growth)  this  layer  of  cells 
[ameloblasts]  remains  upon  a  portion  of  the 
anterior  or  convex  face  of  these  teeth  dur- 
ing the  entire  life  of  the  animal. 

This  constitution  of  the  follicle,  compre- 
hending, as  it  does,  these  three  fundamental 
parts,  seems  to  be  characteristic  of  that  of 
man,  of  the  carnivora,  and  in  general  of  all 
the  mammals  whose  teeth  are  not  supplied 
with  coronal  cement.  But  if  the  follicle  of 
an  embryonal  soliped  be  examined,  it  will 
be  noticed  that  for  a  long  time  before  the 
formation  of  the  first  dentine-cap  there  ex- 
ists between  the  follicular  wall  and  the  or- 
gans within  it  a  new  tissue,  very  distinct 
from  the  neighboring  parts  —  in  color,  in 
consistence,  and  in  composition.  This  is 
the  organ  upon  which  will  subsequently 
depend  the  formation  of  the  cement.  We 
will  omit  the  description  of  the  cemental 
organ  here,  but  will  study  it  elsewhere  in 


OF   THE    DENTAL    I •'<  LLIOLE.  1  1  1 

detail;  all  that  we  wish  to  establish  at 
presenl  is  its  incontestable  existence  in  the 
follicles  of  Buch  teeth  as  are  clothed  with 
corona]  cement.* 

This  fact  is  so  decisive  that  by  the  simple 
examination  of  a  follicle  we  can  determine, 
from  the  presence  or  the  absence  of  this 
organ,  whether  the  future  tooth  will  or 
will  not  be  furnished  with  coronal  cement. 

The  dental  follicle,  the  component  parts 
of  which  are  all  thus  grouped  and  inclosed 
in   one  sac,  has  a  general   ovoid   form.     Its 

*  This  cemental-organ,  which  will  always  be  found  in  the 
follicles  of  the  molars  of  herbivorous  animals,  and  in  those 
of  the  incisors  and  molars  of  solipeds,  has  been  described 
for  the  first  time  in  France,  in  a  work  by  E.  Magitot,  enti- 
tled "  Derelopvment  de  la  Structure  des  Dents."  (These  in- 
augurate, 1858,  p.  80).  It  was  presented  anew  some  years 
ater  by  Robin  et  Magitot.  (Loc.  Cit.  1861,  p.  145  et  suiv.) 
Since  that  time  the  existence  of  this  organ  appears  not  to  have 
been  recognized  by  any  other  anatomist.  Indeed,  in  the 
last  works  published  in  Germany,  by  Kdlliker,  Waldeyer, 
Hertz.  Kollmann  and  others,  its  existence  lias  been  formally 
denied.  We  are  greatly  surprised  to  see  so  evident  an 
anatomical  fact  thus  contested;  but  it  will  be  easy  for  us  to 
establish  again  the  reality  of  this  discovery,  which  we  pro- 
pose doing  in  our  second  memoir. 


112  THE    ORIGIN    AND    FORMATION 

size  varies  greatly  in  the  different  animal 
species,  and  according  to  the  kind  of  teeth 
that  are  to  be  developed  from  it.  When 
the  follicle  is  completely  formed,  it  remains 
inclosed  within  the  embryonal  tissues  of  the 
jaws,  with  which  at  first  it  is  only  feebly 
connected.  Thus  isolated  in  the  depth  of 
the  jaws,  having  lost  its  communication 
with  the  mucous  membrane  [epithelium], 
by  the  rupture  of  the  cord,  it  does  not  yet 
form  any  connection  with  the  maxillary 
bone;  for  the  formation  of  the  alveolar 
partitions  does  not  take  place  until  a  later 
period. 

The  net- work  of  vessels  which  ramify  the 
follicular  wall  and  dental  bulb  is  furnished 
from  different  sources,  and  enters  these 
tissues  from  the  surrounding  parts;  while 
the  enamel-organ,  as  we  know,  is  non- 
vascular. The  direction  of  the  follicle,  that 
is  to  say  the  great  axis  of  the  ovoid,  which 
it  represents,  is  quite  variable.  Though 
regularly  vertical  in  man  and  the  carnivora, 


OF    THE    DENTAL    FOLLK  LE. 


1  L3 


ii  takes  an  oblique  direction  in  the  herbiv- 
orous animals,  and  this  i>  more  particularly 
marked  in  the  follicles  of  the  incisors.  The 
latter,  in  fact,  take  an  oblique  and  diver- 
genl  course,  like  the  spoke-  of  a  wheel, 
which  is  moreover  in  conformity  with  the 
inclination  of  the  alveolar  arch.    (Fig.  28). 


A 


rff.rfi 


My 

MP 


Fig.  28. — Vertical  section  of  anterior  portion  of  the  lower 
jaw  of  an  equine  embryo,  magnified  80  diameters. 

a,  Meckel's  cartilage;  b,  traces  of  ossification;  d,  oral 
epithelium;  g,  enamel-organ;  //,  dental  bulb;  /,  layer  of 
ameloblasts  (internal  epithelium);  K,  permanent  follicle; 
L,  place  assigned  for  the  development  of  the  cement. 


114  THE    ORIGIN   AND    FORMATION 

We  may  add,  however,  that  the  axis 
of  the  follicle  is  generally  the  same  as 
that  of  the  bulb,  and  that  it  strictly  corre- 
sponds with  that  of  the  alveolar  border,  for 
each  particular  species.  As  to  its  position 
in  the  jaws,  it  differs  in  like  manner  accord- 
ing to  the  species.  In  man,  the  carnivora 
and  the  solipeds,  it  is  situated  quite  near 
the  mucous  membrane  [epidermis],  and  in 
these  the  epithelial  cord  is  consequently 
quite  short;  but  it  is  located  more  deeply, 
in  the  bovine  and  ovine  herbivora  (cattle 
and  sheep),  and  the  cord  consequently  ac- 
quires a  proportionate  length. 


OF    THE    DENTAL    FOLLICLE  1  1  5 


CHAPTER  IV. 


PHENOMENA  THAT  FOLLOW  THE  FORMATION  OF  THE 
FOLLICLE,  AND  THE  RUPTURE  of  THE  EPITHELIAL 
CORD. 

AS  soon  .-is  tin*  sac  is  closed,  ami  rh<-  follicle 
-*--^-  becomes  isolated  by  the  rupture  of 
the  epithelial  cord,  various  phenomena  are 
produced  in  the  embryonal  tissues  that  sur- 
round this  organ,  in  the  region  between  the 
summit  or  apex  of  the  follicle  and  the  epi- 
thelial layer  of  the  gum.  These  phenom- 
ena are  principally  located  in  the  epithelial 
lamina  and  in  the  cord  itself. 

In  fact,  as  soon  as  the  epithelial  lamina 
loses  its  connection  with  the  follicle,  by  the 
rupture  of  the  cord,  the  epithelial  cells 
composing  it  become  greatly  increased  in 
number  at  the  severed  point.  This  multi- 
plication of  cell-elements  results  in  the 
format  ion    of    irregular    buddings,    which 


116  THE    OEIGIN    xVND    FORMATION 

wander  in  different  directions  into  the 
deeper  portions  of  the  embryonal  tissue. 
These  buddings  vary  greatly  in  form ; 
sometimes  they  are  simple  cylinders,  retain- 
ing their  connection  with  the  primitive 
lamina  by  pedicles  of  various  lengths,  and 
sometimes  this  slight  connective  is  ab- 
sorbed, thus  isolating  an  epithelial  mass. 
(Fig.  19,  F,  p.  67.) 

These  masses  are  formed  wholly  of  large 
polygonous  cells,  similar  to  those  found  in 
the  center  of  the  epithelial  lamina;  but 
they  are  never,  like  the  latter,  surrounded 
by  a  layer  of  prismatic  cells.  Very  fre- 
quently, however,  groups  of  these  elements 
take  the  globular  form,  and  are,  in  every 
respect,  similar  to  those  which  are  some- 
times discovered  within  the  epithelial  lam- 
ina itself.  (Fig.  29,  F.)  These  different 
dispositions  account  for  the  presence  of 
epithelial  masses  of  such  varied  form ; 
which,  until  now,  were  unexplained,  and' 
which  are  found  in  almost  all  the  sections 
of  the  jaws  made  at  this  epoch  of  evolution. 


OF    THE    DENTAL    I'M. I. KIT. 
Km;.  29. 


117 


*2i    „       tw$jS        r 


Fig.  29.— This  is  a  section  taken  from  an  embryonal 
calf.  (Magnified  260  diameters.)  Like  fig.  19,  it  embraces 
the  region  external  to  the  follicle  (a),  which  latter  is  no! 
shown  on  the  cut;  b,  epithelial  buddings  upon  the  follicular 
wall;  EE,  buddings  of  the  epithelial  cord;  /■'.  globular 
epithelial  mass  in  the  lamina;  ii,  oral  epithelium  (epidermis); 
c,  epithelial  lamina  "  still  intact." 


118  THE    ORIGIN    AND    FORMATION 

These  phenomena  of  buddings  cease  at  a 
certain  period,  which  always  seems  to  be 
anterior  to  the  time  at  which  the  dentine 
makes  its  appearance  in  the  follicle ;  and 
then  all  the  epithelial  fragments,  and  the 
lamina  itself,  undergo  gradual  absorption, 
and  entirely  disappear  before  the  develop- 
ment of  the  tooth  is  perfected. 

Coincidently  with  the  phenomena  thus 
effected  at  the  expense  of  the  ejrithelial 
lamina,  a  series  of  modifications  jDrecisely 
analogous  transpires  also  in  the  severed  cord 
itself.  From  the  remnants  of  this  cord, 
buddings,  or  processes,  issue,  which,  at 
times,  are  very  numerous ;  as  we  have  wit- 
nessed, for  example,  in  certain  preparations 
taken  from  the  jaws  of  bovine  embryos. 
These  phenomena  continue  for  a  consider- 
able length  of  time,  since  they  can  be  ob- 
served up  to  a  period  even  verging  on  the 
eruptive  stage.  The  general  form  of  these 
buddings  may  vary;  sometimes  they  pre- 
sent somewhat  the  appearance  of  a  bouquet, 


OF   THE    DENT  \i.    FOLLICLE.  I  I  9 

(ihc  Pool  corresponding  to  the  summit  of 
the  follicle,.)  which  spreads,  open-  and  con- 
tinue- to  expand  till  it  reaches  the  vicinity 
of  tlif  epidermis  (  Pig.  27,  K  ) ;  a1  other  times 
tlic\  form,  by  a  multitude  of  reciprocal 
anastomoses,  a  perfect  net-work  (Fig.  29, 
E  E),  in  tin-  nii»l>t  of  which  are  still  found 
some  isolated  masses. 

Hut  these  differently  grouped  or  anasto- 
mosing buddings  <!<>  n<>t  all  follow  the  di- 
rection  of  the  lamina,  nor  of  the  cord;  in 
fact  their  general  tendency  is  evidently 
toward  the  surface  of  the  mucous  mem- 
brane. 

The  del>ris  of  the  cord  are  invariably 
composed  of  small  polyhedral  cells  lying  in 
juxtaposition  to  each  other,  and  exactly 
similar  to  those  of  the  cord  itself;  bu1  the 
cells  composing  these  debris,  like  those  of 
the  remains  of  the  lamina,  are  never  in- 
vested with  a  layer  of  prismatic  cells. 

The  buddings  of  the  cord  are  also  of 
variable  size:  some  are  extremely  slender, 


120  THE    ORIGIN    AND    FORMATION 

and  composed  of  a  single  string  of  cells; 
others  assume  a  strumous  or  swollen  form, 
and  contain  several  superimposed  layers  of 
these  elements;  but  the  large  cells  and 
the  globular  masses — the  presence  of  which 
we  have  recognized  in  the  debris  of. the 
lamina  —  are  never  found  here. 

The  remains  of  the  cord,  like  those  of 
the  epithelial  lamina,  after  undergoing  these 
multiplications,  become  gradually  absorbed, 
and  disappear,  as  was  previously  stated,  at 
or  about  the  period  of  eruption. 

While  these  j)henomena  of  buddings  are 
taking  place,  at  the  expense  of  the  debris 
of  the  cord,  it  will  be  noticed  that  a  similar 
process  is  going  on  at  the  exterior  surface 
of  the  follicular  wall.  These  two  series  of 
phenomena,  as  well  as  those  that  take  place 
in  the  lamina,  are  simultaneous."* 

In  fact,  if  a  vertical  section  be  made  of 
the  region  comprised  between  the  summit 

*  All  this  array  of  facts  has  been  presented  for  the  first 
time  in  France,  by  Robin  and  Magi  tot.  (Loc.  cit.,  I860, 
p.  74.) 


01    THE    DENTAL    FOLLICLE  12] 

of  .-i  follicle  and  the  external  surface  of  the 
epidermis,  shorl  ly  after  the  rupture  of  I  he 
cord  has  taken  place,  it  will  be  seeu  thai 
tlir  remnants  of  this  cord  even  extend  t<> 
and  mingle  with  some  of  the  proliferations 
which  arc  adherenl  bo  tin-  wall  |  sac  |.  These 
have  the  most  varied  forms;  mostfrequently 
they  are  club-shaped  expansions,  or  <-\  lin- 
ders  of  different  lengths,  terminating  in  a 
rounded  extremity;  and  sometimes  pro- 
vided with  a  kind  of  pedicle.  They  cover 
nearly  the  whole  surface  of  that  hemisphere 
of  the  follicle  which  is  presented  toward 
the  epidermis.  These  buddings,  however, 
are  most  abundant  at  the  apex  of  the  fol- 
licle [the  point  where  the  cord  was  at- 
tached], and  they  gradually  diminish  as 
they  descend  upon  its  sides.  They  anasto- 
mose transversely  both  with  each  other  and 
with  those  that  are  attached  to  the  cord: 
and  in  such  a  way  that  by  simply  examin- 
ing the  surface  of  the  follicle,  without  mak- 
ing  a  vertical  section,  we  perceive  a  kind 


122  THE    ORIGIN    AND    FORMATION 

of  plexus  with  very  irregular  meshes,  super- 
posed upon  the  follicular  wall.    (Fig.  29,  b.) 

The  auatomic  structure  of  these  bour- 
geons [or  prolongations]  on  the  surface  of 
the  follicle  differs  in  no  respect  from  those 
which  we  have  indicated  in  the  proliferations 
of  the  cord,  being  composed  of  the  same  small 
polyhedral  cells  minus  the  enveloping  pris- 
matic layer.  This  identity  of  structure  results 
from  the  fact  that  these  epithelial  masses 
are  derived  from  the  remains  of  that  portion 
of  the  cord  which  is  in  the  nearest  proximity 
to  the  follicle,  and  which  by  proj3agating 
themselves  thus  finally  constitute  this  retic- 
ular covering  of  the  follicle. 

All  these  phenomena  of  epithelial  pro- 
liferations relate,  therefore,  to  one  and  the 
same  process.  Commencing  with  the  lam- 
ina, these  buddings  extend  to  the  cord,  and 
finally  even  to  the  surface  of  the  follicular 
wall;  they  are  connected  with  each  other, 
possess  the  same  anatomical  constituents, 
and  all  finally  disappear  by  absorption  [un- 


OF    THE    DENTAL    FOLLICLE  1  23 

lesa  it  be  some  masses  that  may  become  fche 
enamel-organs  of  supernumerary  teel  ii.  ( See 
]».  66.)— Tb.] 

Wo  ha. ve  indicated   in  fche  foregoing  fche 
period  at  which  fche  phenomena  of  budding 
commence,  namely,  when  fche  epithelia]  cord 
lias  finished  its  course,   having  conducted 
fche   primitive   enamel-organ  to  that   point 
where  its  subsequent  evolution  will  be  ef- 
fected, and  soon  after  the  formation  of  the 
secondary  follicle;  [in  other  words,  immedi- 
ately after  the  rupture  of  tlfe  cord  of  the 
primitive  follicle].     The  time  of  their  dis- 
appearance varies  in  the  different  species  of 
animals.    In  the  human  embryo  the  remains 
of  the  cord  of  the  primitive  follicles  may  be 
found  even  after  the  formation  of  the  fol- 
licles of  the  permanent  teeth,  and  it  is  prob- 
ably during  the  process  of  eruption   that 
these  buddings  become  atrophied:   in  fche 
canine  embryo  fche  facts  are  nearly  fche  same: 
in  fche  bovine  and  ovine  embryos  (calf  and 
lamb),  it   has  seemed  to  ns  thai   these  pro- 


124  THE    ORIGIN    AND    FORMATION 

liferations  disappear  at  a  correspondingly 
earlier  stage ;  and  we  think  it  safe  to  say 
that,  as  a  general  rule,  the  complete  absorp- 
tion occurs  toward  the  period  of  eruption. 

The  physiological  signification  of  these 
phenomena  appears  to  us  difficult  to  deter 
mine.  We  have  no  personal  opinion  to  ad- 
vance in  this  regard ;  nevertheless  we  will 
say  that,  considering  their  mode  of  evolu- 
tion and  their  structure,  no  glandular  char- 
acter whatever  can  be  attributed  to  them, 
as  some  have  supposed.* 

*  Serres,  as  is  known,  described  what  he  supposed  to 
be  special  glands,  tartaric  glands,  in  the  mucous  mem- 
brane; and  his  views  were  supported  by  Kolliker,  Todd 
and  Bowman,  and  others.  The  anatomical  nature  of  these 
epithelial  masses,  and  the  fact  that  the  production  of  tartar 
is  connected  with  quite  different  phenomena,  leaves  no 
foundation  for  this  hypothesis. 

[I  have  not  the  works  of  Todd  and  Bowman  at  hand, 
but  think  Legros  and  Magitot  must  be  mistaken  in  regard  to 
the  opinion  of  these  authors  upon  this  subject.  As  to  the 
views  of  Kolliker,  in  the  fourth  edition  of  his  Microscopical 
Anatomy,  speaking  of  the  "gum  in  the  foetus, "  he  says: 
"The  bodies  of  the  size  of  a  millet-seed,  contained  in  it,, 
described  by  Serres,  the  so-called  glandulce  tartaricai, 
which  are  supposed  to  secrete  the  tartar  of  the  teeth,  are 


<>l     THE    DENTAL    FOLLICLE.  125 

While  the  modifications  jusl  described 
are  being  effected  at  the  expense  of  the 
epithelial  debits  of  the  cord  and  the  lamina, 
the  embryonic  tissue  in  which  the  follicles 
arc  immersed  also  changes  it-  nature,  and 
some  Laminated  elements  appear  therein, 
forming  a  Loose  and  transparent  aet-work. 

The  osseous  tissue  of  the  jaw  (no  trace, 
of  which  is  seen  at  the  time  of  the  origin 
of  the  primitive  cord)  makes  its  first  ap- 
pearance near  the  base  of  the  follicles, 
where  it  soon  forms  a  horizontal  layer, 
separating  the  groove  of  the  follicles  from 
the  canal  reserved  for  the  vessels  and 
nerves.  Lateral  processes  then  arise  from 
this  Layer  or  floor,  and  form  the  groove  in 

aggregations  of  epithelium,  and  probably  pathological," 
In  his  fifth,  in  place  of  the  words  "  and  probably  patho- 
logical," the  following  are  substituted:  "which,  according 

to  my  recent  observations,  are  the  remains  of  the  embry- 
onal germ  of  the  enamel-organ"  [i.e.,  of  the  epithelial 
lamina].  The  views  of  Kdlliker,  and  Legros  and  Magitot 
are  then  precisely  the  same  on  this  point,  so  tar  as  they 
are  expressed  in  these  works,  the  only  difference  being  in 
the  form  of  expression. — Tk.J 


126  THE    ORIGIN"    AND    FORMATION" 

which  the  follicles  lie  for  some  time  with- 
out being  separated  by  transverse  parti- 
tions. But  later,  after  the  development 
of  the  crowns  of  the  teeth  has  commenced^ 
bony  processes  are  thrown  across  this 
groove,  forming  cells  for  the  lodgment  of 
each  follicle,  with  an  opening  toward  the 
epithelial  surface. 

A  rich  vascular  network  of  tissue  'sur- 
rounds the  follicle,  and  ramifies  the  sub- 
stance of  the  walls  even  to  the  surface  of 
the  enamel-organ,  but  does  not  penetrate  it. 

The  vessels  of  the  bulb  are  entirely  dis- 
tinct, forming  no  anastomosing  connection 
with  the  preceding  plexus.  We  shall,  how- 
ever, have  occasion  to  refer  to  these  particu- 
lars hereafter,  in  treating  of  the  morphology 
and  structure  of  the  follicle. 


OK     IIIK    DION  I'M-    lol.l.irl.K.  1  -7 


CHAPTER  V. 


THE    PLACE,   AM)    MODE  OF  ORIGIN,   OF   THE    FOLLICLES 
OF  THE    PERMANENT  TEETH. 

r  I  T 1 1 E  origin  of  the  follicles  of  the  per- 
-■-  manent  teeth  is  a  problem  that  1ms 
received  particular  attention  from  the  more 
recent  authors  who  have  studied  the  evolu- 
tion of  the  teeth.  It  is  one  which  we  also 
have  examined  with  the  greatest  care  and 
]>;itience;  and  we  believe  we  have  suc- 
ceeded in  sol  vino;  it  correctly. 

Since  the  publication  of  the  works  of 
Goodsir  —  in  which  that  author  held  that 
the  follicles  of  the  permanent  teeth  arise 
from  a  fold  of  the  sac  of  the  primitive 
follicle  —  most  anatomists  have  adopted  his 
theory  without  examination  or  verification. 
This  doctrine  is  no  more  in  conformity 
with  the  tacts  than  is  the  theory  that  the 


128  THE    ORIGIN   AND    FORMATION 

sacs  of  the  temporary  teeth  are  formed  by 
an  inversion  of  the  mucous  membrane.  We 
have  already  given  our  views  in  regard  to 
this  hypothesis,  and  we  will  refer  to  it 
again  at  the  close  of  this  work.  The 
theory  of  Goodsir  will  be  found  as  errone- 
ous in  regard  to  the  permanent  as  it  is 
to  the  temporary  teeth. 

We    ought   to   mention,    however,    that 
Kolliker  and  Waldeyer   have   come   near 
the    truth    in    indicating    and   illustrating 
certain  prolongations  of  the  primitive  cord, 
which  are  destined  to  become  the  secondary 
cord.     But  in  the  most  recent  work  pub- 
lished in  Germany,  that  of  Kollmann,  the 
preceding   interpretation  is  not   adopted.* 
According  to  the  views  of  this  anatomist, 
the  cord  of  the  permanent  teeth  arises  from 
the  remnants  of  the  primitive  cord,  which, 
after   its   rupture,   produces   those    several 
buddings    or   epithelial   masses  which  we 
have  already  described.    He  believes  that 

*  Kollmann,  loc.  cit.,  p.  162,  etc. 


OF   THE    DENTAL    FOLLICLE.  1  29 

the  enamel-organ  of  the  permanent  fcooth 
originates  from  a  mass  of  those  epithelial 
fragments.  In  a  Like  manner  he  accounts 
for  the  production  of  the  supernumerary 
teeth.*  This  new  theory  is  equally  errone- 
ous; and  if  this  German  author  lias  been 
deceived  by  certain  natural  appearances, 
which  might  favor  his  opinion,  it  is  because 
he  has  neglected  to  follow  out  strictly,  in 
their  successive  physiological  phases,  the 
phenomena  of  this  special  evolution. 

Furthermore,  the  origin  of  those  perma- 
nent follicles  that  have  been  preceded  by 
corresponding  temporary  ones,  is  altogether 
different  from  that  of  those  which  had  no 
such  predecessors;  so  that  while  all  of  the 
twenty  follicles  of  the  permanent  teeth  that 
succeed  the  twenty  temporary  ones  have  a 
like  origin,  the  twelve  other  foUicles  (the 
molar-  of  the  adult)  have  a  different  mode 
of  genesis.  |  I'>\  this  these  author-  mean,  as 
will  lie  -ecu  hereafter,  that  (ill  the  enamel- 
Bee  note.  pp.  65-6  of  this  work. — Tk.] 


130  THE    OBIGIN    ATSTD    FORMATION 

organs  of  the  permanent  teeth  except  those 
of  the  first  molars,  originate  from  the  epi- 
thelial cords  of  other  follicles,  and  not  di- 
rectly from  the  epithelial  lamina  itself. — 
Te.] 

The  facts  we  are  about  to  advance  have 
been  gathered  from  the  examination  of  a 
large  number  of  mammalian  embryos,  com- 
prising a  series  of  successive  phases  of  de- 
velopment. In  studying  microscopical  sec- 
tions taken  from  the  jaws  of  human  embryos 
measuring  twenty  centimetres  from  crown 
to  heel,  a  bourgeon  will  be  found  at  the 
point  where  the  primitive  cord  merges  into 
the  enamel-organ  of  the  temporary  tooth. 
The  general  form  of  this  bourgeon  is  cylin- 
drical, terminating  in  a  somewhat  enlarged 
extremity,  which  gives  it  a  clubbed  or  gourd- 
like shape  at  this  stage  of  evolution  (Fig. 
30,  K),  and  may  be  seen  quite  distinctly 
with  a  low  magnifying  power  of  100  to  200 
diameters.  [Fig.  22,  K,  represents  this  bour- 
geon at  an  earlier  period].   It  takes  a  general 


OF   THE    DENTAL    l<  l.l.h  l.K. 


i.;i 


vertical  direction,  and   passes  between  the 
osseous  alveolar  wall  and  the  primitive  fol- 


PlG.  30. — Section  of  the  lower  jaw  of  a  human  embryo, 
total  length  30  centimeters,  or  about  8  inches;  taken  from 
the  region  of  the  follicle  of  the  temporary  molar  (magnified 
80  diameters). 

A',  cord  of  the  permanent  follicle,  "emanating"  from 
that  of  tin-  temporary  molar;  /•.'.  eriamel-organ;  /•'.  cord  of 
the  temporary  follicle;  //.  dentine-bulb;  /.  follicular  wall: 
«,  Meckel's  cartilage:  r  (upper),  section  of  the  dental  artery: 
c  (lower I.  that  of  the  dental  nerve;  d,  epithelial  cells. 


132  THE    ORIGIN    AND    FORMATION 

licle,  along  the  internal  or  lingual  face  of 
the  latter.  The  elements  of  which  it  is  com- 
posed are  the  same  as  those  of  the  primitive 
cord,  of  which  it  is  in  reality  only  a  divertic- 
ulum or  out-growth ;  that  is,  of  polygonons 
cells  covered  with  a  single  layer  of  prismatic 
ones. 

This  bourgeon  or  bud  represents  the  be- 
ginning of  the  permanent  tooth ;  and  after- 
it  has  become  sufficiently  developed,  one 
can  easily  follow  the  subsequent  phenomena 
of  which  it  is  the  seat.  It  sinks  to  the  bot- 
tom of  the  osseous  dental  groove,  where  it 
soon  loses  its  connection  with  the  primitive 
follicle,  though  still  retaining  its  communi- 
cation with  the  lamina ;  while  the  primitive 
follicle,  by  the  severance  of  its  cord  (which 
takes  place  just  below  the  point  where  the 
secondary  cord  branches  off),  becomes  iso- 
lated from  its  epithelial  connection  and  con- 
tinues its  individual  evolution.    (Fig.  31.) 

It  was,  doubtless,  by  examining  the  jaws 
at  the  stage  of  development  just  referred  to, 


OF     NIK    DKNTA  I-     FOLLICLE. 


L33 


without  taking  into  accounl  the  earlier  and 
Later  phases,  that  led  to  the  belief  thai  the 
cord  of  the  permanenl  teeth  emanated  from 


l'i...   81. 


Fie  31. — Section  of  tin-  lower  jaw  of  a  human  foetuB, 
23  centimeters  in  length  [or  01.,  inches;  corresponding  to 
about  the  18th  week]. 

K,  cord  or  bourgeon  of  the  permanenl  follicle;  L,  point 
where  its  separation  from  the  primitive  cord  is  being 
effected:  g,  enamel-organ;  //.  bulb;  c,  section  of  the  dental 
artery;  b,  traces  of  ossification;  c,  (lower)  nerve;  a,  Meckel's 
cartilage. 


134  THE    ORIGIN    AND    FORMATION 

the  debris  of  the  primitive  cord,  or  directly 
from  the  epithelial  lamina.     (Fig.  32,  K.) 
The  descent  of  the  secondary  bourgeon 

Pig.  32. 


Zr--:^-—       rs     %m^_ 


^B-l) 


Fig.  32. — Vertical  cut  of  the  lower  jaw  of  a  human  foetus, 
measuring  47  centimeters  [18^  inches,  and  corresponding 
to  about  the  39th  week  of  gestation].  This  figure  represents 
a  section  passing  through  the  follicle  of  a  bicuspid.  K'  K', 
epidermal  masses;  K,  debris  of  the  secondary  cord;  g,  en- 
amel-organ; H,  bulb;  b,  bone  of  the  jaw;  d,  epidermis. 


OF    THE    DKNTAL    FOLLtt  LB.  1  35 

into  the  dental  groove  is  soon  followed  by 
the  entire  Beries  of  phenomena  which  are 
common  to  everj  follicular  evolution,  .  .  . 
[and  which  are  precisely  the  same  as  those 
already  described  for  the  primitive  bour- 
geons. |     (  Pig.  32,  K.) 

While  these  phases  of  development  are 
being  accomplished,  certain  modifications 
occur  in  the  parts  which  Burround  the  prim- 
itive follicle.  The  stump  of  the  ruptured 
cord,  which  remains  attached  to  the  prim- 
itive follicle,  becomes  the  source  of  those  frag- 
mentary growths  and  buddings  which  have 
been  described  at  considerable  length  in  a 
preceding  paragraph.  These  phenomena 
commence  in  the  human  embryo  when  it 
has  attained  about  twenty-three  centimeters 
[or  nine  and  one-fourth  inches]  in  length, 
about  the  fourth  month.  These  phenom- 
ena, which  always  commence  front  the  mo- 
ment the  cord  is  severed,  seem  to  occur  in 
the  embryos  of  other  mammals  a  little 
earlier,  relatively,  in  tin1   period   of  gesta- 


136  THE    ORIGIN    AND    FORMATION 

tion.  This  is  the  case  in  equine  and  bovine 
embryos.  Besides,  in  the  lower  animals 
the  secondary  bourgeon  emanates  from  the 
primitive  cord  at  a  point  a  little  farther 
from  the  primitive  follicle  than  in  the  hu- 
man species.  This  is  also  the  case  in  the 
ovine  embryo. 

Casper  :  I  have  just  been  reading  a  treatise 
styled  the  Anatomical,  Physiological  and  Mi- 
croscopical Researches  on  the  Teeth,  by  Dr.  J.  E. 
Oudet,  a  French  writer,  whose  opinion,  it  seems 
to  me,  is  entitled  to  considerable  respect.  He 
most  emphatically  denies  that  any  of  the  perma- 
nent follicles  are  derived  either  from  the  cords  or 
from  follicles  of  the  temporary  teeth ;  on  the 
contrary,  he  claims  that  they  emanate,  directly 
and  independently,  from  the  "  mucous  mem- 
brane." It  seems  very  strange  that  there  should 
be  such  wide  differences  of  opinion  in  regard  to 
a  simple  anatomical  fact. 

Teacher:  Nearly  all  of  the  most  eminent 
histologists  of  the  present  day, — Tomes,  Kolliker, 
Waldeyer,  Frey,  Owen,  Wedl,  and  I  know  not 
how  many  others,  entertain  essentially  the  same 
views  in  regard  to  this  phenomenon  as  are  here 


OF    THE    DENTAL    FOLLICLE.  137 

set  forth  by  Drs.  Legros  and  Magitot.  There  are, 
however,  a  few  distinguished  writers,  foremost 
among  whom  is  the  author  you  named,  who 
believe  that  all  the  permanenl  teeth  originate 
independently  of  the  temporary  set.  Then, 
#  again,  we  have  one  histologist,  our  neighbor,  Dr. 
(t.  \r.  Black,  of  Illinois,  whose  extensive  obser- 
vations in  this  direction  have  convinced  him 
that,  although  tin-  epithelial  c<>r<ls  of  the  twenty 
anterior  permanent  teeth  generally  arise  front 
those  of  the  temporary  follicles,  yet  that  they 
do  sometimes  emanate  directly  from  the  epi- 
thelial lamina.  It  would  appear  from  fig.  30, 
and  also  fig.  31.  in  the  Summary  of  Illustra- 
tions (drawings  of  which  were  kindly  fur- 
nished me  by  this  gentleman),  that  his 
views  are  demonstrated  beyond  question.  The 
histological  specimens  from  which  these  draw- 
ings were  taken  have  been  examined  by  my- 
self and  others;  and,  saving  a  few  minor  and  un- 
important details,  they  are  faithfully  represented 
in  these  cuts.  I  have  the  assurance  of  Dr. 
Black  that  these  were  taken  by  himself  from 
the  inciswi  region  of  different  human  embryos. 

In     these     figures    the     epithelial     COl'ds     of     the 

permanent   follicles  appear   to   emanate   directly 
10 


138  THE    ORIGIN    AND    FORMATION 

from  the  lamina;  in  figs.  32  and  35,  from  the 
•epithelial  cord  ;  and  in  figs.  26,  27  and  28,  from 
the  primary  follicle  itself,  rather  than  from  its 
eord.  (For  these  five  figures,  also,  see  Summary.) 
If  all  these  figures  are  true  representations  of 
the  parts  themselves,  the  secondary  cord  may 
emanate  directly  from  either  the  lamina,  the 
cord,  or  the  follicle  itself. 

Now,  one  word  as  to  the  place  of  origin  of  the 
third  permanent  molar.  I  am  not  prepared  with 
any  positive  proof  that  this  does  not  emanate 
from  the  source  attributed  to  it  by  the  authors 
of  this  work,  and  also  by  the  several  eminent 
authors  first  named,  except  Wedl.  In  closing 
these  remarks  I  will  only  say  that  when  I  con- 
sider the  distance  and  the  direction  that  this 
cord  must  pursue, —  starting  from  the  point  on 
the  lamina  from  which  the  first  molar  arises, 
and  extending  in  a  backward,  horizontal  line 
fo  the  spot  where  it  eventually  is  developed; 
and,  when  I  take  into  account  the  period  of 
time  that  this  cord  must  retain  its  normal 
attachment  to  this  remote  point  in  the  epithe- 
lial lamina  before  the  development  of  this 
follicle  commences, — which  cannot  be  less  than 
three  and  one-half  years;    and  when  I  add  to 


OF   THE    DENTAL    FOLLICLE.  1  39 

these  t'aets  the  great  morphological  changes 
that  occur  in  the  neighboring  and  rapidly-de- 
veloping parte  during  this  long  interval  of 
time; — in  view,  I  say,  of  all  these  unfavorable 
circumstances,  I  am  not  prepared  to  accept 
the  theory  advanced  by  these  celebrated  anat- 
omists in  regard  to  the  origin  of  the  wis- 
dom teeth,  without  more  positive  evidence  to 
sustain  it.  My  own  observations  on  this  sub- 
ject have  not  been  conducted  with  sufficient 
scientific  accuracy  to  justify  me  in  placing  my 
conclusions  (or  convictions)  on  record  here;  but 
I  hardly  need  say  that  these  points  in  embry- 
onal histology  require   much  careful  revision. 

Some  differences  are  observed  also  as 
regards  the  direction  of  this  secondary 
cord  in  the  different  species.  Thus,  while 
in  the  human  embryo  we  have  noticed 
that  it  takes  a  vertical  direction,  in  those 
of  the  herbivora  it  follows  a  very  ob- 
lique course;  so  that  from  the  external 
side  (not  far  from  its  connection  with  the 
epithelial  lamina),  passing  above  the  tem- 
porary follicle,  it  pursues  a  curvilinear  route 


140  THE    ORIGIN    AND    FORMATION 

to  the  internal  or  lingual  face  of  that 
follicle.  This  arrangement  of  the  parts 
may  be  seen  clearly  defined  in  sections 
taken  from  the  incisive  region  of  bovine, 
ovine  and  equine  embryos. 

The  point  upon  the  primitive  cord  from 
which  this  secondary  bourgeon  emanates, 
as  also  the  direction  it  takes,  are  not  neces- 
sarily governed  by  the  length  of  the  sec- 
ondary cord ;  for  in  the  human  embryo,  al- 
though its  direction  is  vertical,  it  is  longer 
than  in  the  equine,  in  which  it  takes  a  cir- 
cuitous course.  As  a  general  rule,  its 
length  is  governed  by  the  height  of  the 
alveolar  border  and  the  direction  of  the 
primitive  follicle.  In  man  and  the  car- 
nivora  this  height  is  relatively  more  con- 
siderable ;  and  besides,  the  great  obliquity 
that  the  primitive  follicles  of  the  incisors  of 
the  herbivora  assume,  allows  the  secondary 
bourgeon  to  cross  directly  over  the  maxilla, 
'and  to  place  itself,  after  a  very  short  pas- 
sage,  on  the  internal  side  of  the  primitive 
follicle,  where  its  evolution  is  completed. 


OF    ill  1-:    DENTAL    FOLLICLE.  141 

The  cord  of  the  secondary  follicle,  in  it> 
descent  into  the  jawsj  always  assumes  a 
spiral  form,  and  thus  perfectly  resembles 
the  duct  <>t"  the  sudorific  gland  in  the 
epidermis.  This  special  disposition  is  so 
marked  a  characteristic  in  the  secondary 
cord,  that  it  may  be  readily  distinguished 
from  the  temporary  cord:  for  though  the 
latter  describes  some  sinuosities  in  its 
course,  it  is  never  so  distinctly  spiral 
as  the  former.  The  necessity  for  this 
greater  spvraMty  in  the  cord  of  the  perma- 
nent follicle  may  be  explained  l>v  the  fact 
that  it  must  traverse  the  more  developed 
tissue  of  the  jaw  to  a  greater  distance  in 
attending  this  follicle  in  its  passage  to  a 
point  beneath  that  of  the  temporary  tooth; 
[and  also  to  allow  the  rapidly  developing 
parts  to  increase  the  distance  between  the 
follicle  and  the  epithelial  lamina,  without 
straining  the  cord  or  disturbing  the  parts 
I"  which  its  two  ends  are  attached. — Tr.1 

The    spiral    character    of    the    secondary 


142  THE    ORIGIN    AND    FORMATION 

cord  is  especially  obvious  near  its  point  of 
origin,  and  in  the  first  half  of  its  course ; 
but  toward  its  terminal  extremity  it  dimin- 
ishes, and  finally  disappears  entirely,  giving 
place  to  a  rounded  club-shaped  enlargement 
exactly  like  that  which  we  have  described 
at  the  extremity  of  the  primitive  cord. 
This  enlargement  or  expansion  represents 
the  enamel-organ  of  the  permanent  tooth. 

When  the  series  of  evolutionary  phenom- 
ena has  brought  the  new  follicle  to  the 
period  in  which,  in  the  human  embryo,  for 
example,  the  bulb  becomes  wnicuspid  for 
the  canines  and  incisors  and  multicuspid  for 
the  molars,  the  epithelial  cord,  which  has 
already  been  sometime  severed  from  the 
primitive  follicle,  becomes  in  its  turn  rupt- 
ured. From  this  period  the  secondary  fol- 
licle, as  well  as  the  primitive,  is  found  iso- 
lated from  all  connection  with  the  epithelial 
lamina  during  the  subsequent  phases  of  its 
evolution. 

This  rupture  is  soon  followed   by  new 


OF     l  III     DENTAL    FOLLICLE.  14.*'. 

subdivisions  in  the  substance  <>t  the  cord 
itself,  which  seems  to  separate  into  frag- 
ments of  various  sizes.  These  fragments 
Lengthen  and  l>u<l  in  different  directions 
to  such  a  degree  thai  these  epithelial  pro- 
cesses ;ir<-  mingled  and  confounded  with 
those  of  the  primitive  cord,  anastomosing 
with  them,  to  form  in  this  region  a  sort  of 
plexus,  sometimes  quite  close,  and  which 
extends  .veil  to  tlie  buddings  that  cover  the 
follicular  wall.  Finally  all  these  epithelial 
mas-.--,  after  having  thus  proliferated  and 
"  vegetated,15  atrophy  and  disappear. 

Such  is  the  mode  of  genesis  of  the  fol- 
licles of  those  permanent  teeth  which  are 
preceded  by  corresponding  temporary  ones. 
Twenty  of  the  teeth  thus  originate.  But 
we  find  that  the  first  teeth  that  appear 
behind  the  deciduous  sel  are  produced  1>\ 
an  entirely  different  mod'-  of  genesis.  The 
first  permanent  molar,  the  follicle  of  which 
become-  considerably  developed  in  foetal 
life,  is  derived  from  an  epithelial  cord  which 


144  THE    ORIGIN    AND    FORMATION 

originates  directly  from  the  epithelial  lamina. 
This  cord  penetrates  the  foetal  tissue  in  a 
region  where  no  follicle  has  preceded  it. 
(Sum,  of  Illus.,  Fig.  39.) 

The  origin  of  the  second  molar  is  similar 
to  that  of  the  first  twenty  permanent  teeth, 
the  follicle  being  produced  from  a  diver- 
ticulum or  outgrowth  of  the  cord  of  the 
first  molar.  In  this  respect  the  second  mo- 
lar sustains  the  same  relation  to  the  first, 
that  the  permanent  tooth  does  to  the  cor- 
responding deciduous  one.  But  they  differ 
in  the  direction  taken  by  the  epithelial 
cords ;  for,  while  those  derived  from  the 
cord  of  the  temporary  follicle  pass  over-  the 
lingual  face  of  the  latter  to  a  point  beneath 
them,  that  of  the  second  molar  takes  a  hori- 
zontal course  for  some  distance,  and  then  by 
an  inflection  takes  its  position  at  the  posterior 
side  of  the  follicle  of  the  first  molar,  where 
it  is  developed  in  a  line  with  those  anterior 
to  it,  (Sum.  of  Illus.,  Fig.  35.)  As  regards 
the  last  molar,  or  tvisdom  tooth,  its  origin  is 


OF    THE    DENIAL    FOLLICLE.  I  15 

effected  in  a  manner  similar  to  thai  which 
we  have  just  described  ;  thai  is,  the  epithelial 
cord  that   produces  its  enamel-organ  is  an 

emanation  from  the  cord  of  the  second  molar. 
We  must  acknowledge,  however,  that  in 
determining   the  origin    of  this  tooth   we 

have  encountered   many   difficulties,  owing 

to  its  position  and  to  the  alteration  in  the 
tissue-,  caused  by  the  many  reactions  to 
which  the  jaws,  after  they  have  acquired 
considerable  size  and  hardness,  must  neces- 
sarily be  submitted.  And  yet,  we  have,  in 
several  cases,  been  enabled  to  determine, 
with  almost  positive  certainty,  that  the 
cord  of  the  wisdom  tooth  originates  in  the 
manner  we  have  already  indicated.  From 
these  observations  we  perceive  that,  while 
the  first  molar  originates,  as  we  have  seen, 
from  the  epithelial  lamina  itself,  it  becomes, 
through  the  medium  of  its  cord,  the  source 
from  which  the  follicles  of  the  succeeding 
molars  are  derived. 
However  this  may  be,  with  these  excep- 


146  THE    ORIGIN    AND    FORMATION 

tions  in  the  mode  of  genesis  of  the  follicles, 
all  the  evolutionary  phenomena  are  iden- 
tical, to  whichever  dentition  they  may  be- 
long; nevertheless  the  order  in  which  their 
evolution  is  accomplished  and  the  duration 
of  their  physiological  phenomena  differ. 
For,  while  the  follicles  of  the  first  dentition 
are  developed  during  the  period  embraced 
between  the  latter  part  of  the  third  month 
of  gestation  and  the  beginning  of  the  fourth 
war  (within  forty-two  months),  most  of 
the  follicles  of  the  second  dentition  require 
a  much  longer  time  for  their  evolution. 
For  example,  though  the  follicle  of  the 
first  molar  makes  its  appearance  in  the  fif- 
teenth week  of  embryonal  life  (and  only  a 
few  days  after  the  most  of  th<:»e  of  the  first 
dentition ).  yet  it  d<>es  not  complete  its  evo- 
lution until  about  the  sixth  year.  We  see, 
therefore,  that  though  the  evolutionary 
phenomena  of  the  follicles  are  identical  in 
other  respects,  they  cover  periods  that  vary 
according  to  the  nature  and  the  temporal) 
or  permanent  character  of  the  future  teeth. 


OF    TIIK    DKNTAL    FOLLICLE.  147 


CHAPTER  VI. 


CHRONOLOGY  OF  THE  DENTAL  FOLLICLE,  OR  THE  PERIODS 
IN  WHICH  ITS  SEVERAL  COMPONENT  PARTS  APPEAR. 

TN  pursuing  our  researches  on  the  mode 
-*"  of  formation  of  the  dental  follicle  in 
mammals,  we  have  constantly  kept  in  view 
one  important  question,  namely,  the  deter- 
mination of  the  periods  at  which  the  sev- 
eral organs  that  enter  into  its  constitution 
make  their  appearance.  This  study  has 
necessitated  the  careful  examination  of  a 
large  number  of  embryos,  both  human  and 
of  the  principal  domestic  mammals.  An- 
other fact  to  be  ascertained  was,  the  exact 
age  of  the  subjects  upon  which  our  observa- 
tions were  made.  This,  in  the  absence  of 
positive  evidence  as  to  the  period  of  concep- 
tion, must,  in  most  eases,  be  determined  by 
measurement.     Xow.  while  the  relation  be- 


148  THE    ORIGIN    AND    FORMATION 

tween  the  size  and  the  age  of  the  human 
embryo  has  been  determined  with  great 
accuracy,  by  the  aid  of  statistics  collected 
from  the  reports  of  various  authors ;  yet,  up 
to  the  present  time  no  sufficiently  accurate 
data  of  this  nature  have  been  given  con- 
cerning the  other  species  of  mammals  in 
their  successive  stages  of  embryonal  life. 
In  the  human  species,  (the  study  of  which 
affords  us  more  interest  than  that  of  any 
other,  and  may  be  more  usefully  applied,) 
we  have  made  numerous  observations  upon 
a  series  of  embryos  measuring  from  8  to 
37  centimetres  \\\  to  15  inches]  in  length, 
i.e.  from  the  seventh  to  the  twenty-eighth 
week  of  intra-uterine  life.  From  these  we 
have  been  enabled  to  fix  all  the  periods 
of  the  evolution  of  the  follicles  of  the  first, 
and  some  of  those  of  the  second,  dentition. 
We  have  established  the  other  phases  of 
the  second  dentition  by  the  study  of  sub- 
jects in  the  later  stages  of  fcetal  life,  and  at 
different  periods  after  birth. 


OF   THE    DENTAL    FOLLICLE.  1 4!> 

The  smallest  of  these  embryos,  thai   of 
3  centimeters  |  1 J  inches],  (seventh  week,) 

from  which  we  have  made  vertical  sec- 
tions through  the  entire  Pace  (Pig.  7). 
has  enabled  us  to  determine  that  at  this 
period  no  point  of  ossification  is  yet  found 
upon  any  part  of  the  cranium  or  of  the 
face;  the  lower  jaw  alone  presents  some 
rudimentary  osseous  arches  in  tin-  vicinity 
of  Meckel's  cartilage.  This  fact  is  in  con- 
formity with  the  observations  published  in 
n  memoir  on  Meckel's  cartilage,  in  1862,  by 
Drs.  Robin  and  Magitot. 

At  this  period  in  embryonal  lite  the  jaws 
otter  nothing  for  our  consideration,  relating 
to  the  evolution  of  the  follicles,  except  the 
epithelial  band,  which  is  Pound  to  be  alike 
in  both  jaws  (Fig.  7),  ami  which  we  have 
already  described.  The  follicle  has  not  as 
yet  appeared  in  these  rudimentary  parts, 
nor  even  the  first  trace  of  the  epithelial 
lamina. 
The   second    embryo   submitted    to   our 


150  THE    ORIGIN    AND    FORMATION 

observation  was  5^  centimetres*  [2£  inches] 
in  -length,  say  of  two  months.  From  this  we 
ascertain  that  the  formation  of  the  dental 
groove  commences  at  this  period  of  develop- 
ment, and  that  the  epithelial  cords  represent- 
ing the  enamel-organs  are  very  clearly  de- 
fined ;  the  dental  bulb  has  already  made  its 
appearance  as  an  opaque  point  in  the  region 
previously  designated  as  its  place  of  origin. 
This  period  of  development,  compared  with 
the  preceding,  has  enabled  us  to  fix  the 
time  of  the  appearance  of  the  epithelial 
lamina  between  the  seventh  and  eighth 
weeks  of  embryonal  life;  and  the  genesis 
of  the  enamel-organ  from  the  epithelial 
cord,  about  the  eighth  week. 

Moreover,  from  these  examinations  we 
have  been  able  to  determine  the  important 
fact  that  development  progresses  at  the 
same  rate  in  both  jaws,  as  well  as  in  all  the 
follicles  of  the  first  dentition,  whether 
they  be  of  the  incisors,  the  canines  or  the 

*  [A  centimetre  =  0.39371,  or  say  \  of  an  inch;  a  milli- 
metre is  TV  of  this,  or  ^  of  an  inch.— Tr. 


OP    THE    DENTAL    FOLLICLE.  L51 

molars.  Upon  a  third  embryo,  which 
measured  71  centimetres  [3  inches],  cor- 
responding to  the  eleventh  week,  we  dis- 
covered  thai  the  stages  of  development 
for  each  of  the  follicles  of  the  first  den- 
tition were  identical,  and  that  the  bull) 
had  become  uni-eit.yid  for  the  incisors  and 
canines,  and  rmdti-ciLspid  for  the  molars. 
The  walls  which  had  already  risen  from 
the  base  of  the  bulb  were  not  yet  united 
at  the  summit  of  the  follicle,  and  the  epi- 
thelial cord  was  still  entire.  The  bulb 
now  consists  of  amorphous  matter  inter- 
spersed with  nuclei,  though  its  external 
surface  presents  a  membranous  appearance. 
The  enamel-organ  is  distinctly  stellated,  and 
the  cells  that  constitute  the  external  epi- 
thelium are  becoming  smaller  as  compared 
with  those  of  the  internal  epithelium  [the 
ameloblasts].  No  trace  of  the  secondary 
cord  is  ye1  aeen. 

From   our  observations  on  a   fourth    em- 
bryo,   of    11    centimetres    [4$   inches  |,   sa\ 


152  THE    ORIGIN    AND    FORMATION 

of  twelve  weeks,  we  ascertained  that  at 
this  period  the  follicular  walls  are  not- 
closed,  and  that  no  trace  of  the  dentine- 
cap  is  yet  visible.  The  next  embryo 
examined  (measuring  15  centimetres  [6- 
inches],  indicating  thirteen  weeks,)  showed 
no  perceptible  difference  in  development 
as  compared  with  the  former. 

In  an  embryo  of  20  centimetres  [8- 
inches]  (say  at  the  commencement  of  the 
fourth  month)  we  collected  some  valuable 
facts  in  regard  to  certain  ulterior  phases  of 
evolution. 

At  this  epoch  the  primitive  follicular 
cord  has  not  yet  become  severed,  nor  the 
follicle  closed.  A  little  cap  of  dentine  is 
seen  very  clearly  outlined  in  some,  though, 
not  in  all,  of  the  follicles  of  the  temporary 
dentition.  It  is,  in  fact,  at  the  exact  period! 
when  a  slight  trace  of  ivory  is  formed  that 
we  discovered  the  first  chronological  differ- 
ence in  the  development  of  the  follicles  of 
the  temporary  teeth.     For  while  the  inci- 


OF    THE    DENTAL    FOLLICLE.  153 

sors  and  the  canines  are  now  pro\  ided  with 
a  cap  of  embryonal  dentine,  it  does  noi  ap- 
pear upon  the  molars  until  about  a  week 
later.  The  l>ull>  [dentine-germ]  has  now 
the  exact  form  of  the  crown  of  the  future 
tooth;  its  base  has  already  become  con- 
stricted and  is  embraced  by  the  margins  of 
the  enamel-organ,  which  is  already  com- 
pletely constituted,  with  its  internal  layer 
of  cells  [ameloblasts],  and  the  stratum  >n- 
t<  rmedium  well  defined. 

It  is  also  at  this  period  <>f  development 
that  we  first  sec,  emanating  from  the  primi- 
tive cord,  those  buddings  which  are  des- 
tined to  form  the  secondary  cords,  or  the 
enamel-organs  of  the  permanent  teeth.  All 
these  bourgeons  (or  buds)  representing  the 
commencenienl  of  the  permanent  follicles. 
are,  in  both  jaws,  at  the  same  stage  of  evo- 
lution |  in  other  words  these  enaniel-lmds 
stall  simultaneously  ]. 

From  an  embryo  of  nearly  the  same  di- 
mensions as  the  preceding  (23^  centimetres 
11 


154  THE    ORIGIN    AND    FORMATION 

[9£  inches]  in  length,  and  corresponding  to 
the  eighteenth  or  nineteenth  week),  we  have 
fixed  the  epoch  at  which  the  separation  of 
the  secondary  cord  from  that  of  the  primi- 
tive follicle  takes  place.  The  latter  now 
becomes  isolated  from  the  epithelial  lamina 
and  continues  its  evolution  without  any 
further  connection  with  this  tissue.  (Fig. 
31,  p.  133.)  The  permanent  follicle,  how- 
ever, still  remains  attached  to  the  cord,  and, 
by  the  lajbter,  to  the  epithelium.  We  direct 
attention  to  these  facts,  because  in  neglect- 
ing to  take  account  of  the  successive  phases 
of  evolution  one  might  be  led  to  believe 
that  the  follicles  of  the  permanent  teeth 
originate  directly  from  the  epithelial  lamina, 
and  not  from  the  cords  of  the  temporary 
teeth.  This  last  mode  of  genesis  is,  on  the 
contrary,  definite  and  invariable  for  all  the 
follicles  of  the  permanent  teeth  which  have 
been  preceded  by  corresponding  temporary 
teeth,  that  is  to  say,  for  twenty  of  the  teeth 
of  the  second  dentition;  viz.,  the  eight  in- 


OF   Tin:    iiknta  L    FOLLI4  LE.  1  55 

cisors,  tlic  four  (•.•mine--  and  the  eight  pre- 
molars [bicuspids].  It  will  be  seen  thai 
the  other  follicles  of  the  permanent  teeth 
have  a  diiferenl  origin.  The  sections  taken 
from  the  jaws  df  the  embryo  (  l'"  centi- 
metres in  Length)  have  enabled  us  t<>  deter- 
mine positively  tin-  period  and  tin-  mode  <»f 
genesis  <>f  the  cord  of  the  first  permanent 
molar,  which  is  not.  as  is  known,  preceded 
by  a  corresponding  temporary  tooth.  This 
genesis  takes  place  at  the  extremity  of  the 
epithelial  lamina;  and  since,  in  the  embiyo 
above  named,  the  epithelial  cord  had  al- 
ready acquired  considerable  length,  we 
may  reasonably  conclude  that  its  develop- 
ment commenced  about  the  seventeenth 
week  of  gestation.     (Fig.  39,  ISumma/ry.) 

At  this  epoch,  when  the  separation  of 
the  temporary  follicles  from  the  cord  of  the 
corresponding  permanent  ones  takes  place, 
there  appears  also  the  firsl  trace  of  those 
phenomena  of  buddings  and  of  divers  pro- 
liferations of  the  debris  of  this  primitive 


156  THE    ORIGIN    AND    FORMATION 

cord  and  of  the  epithelial  masses  on  the 
walls, —  particularities  which  were  first  de- 
scribed in  France.*  By  the  examination  of 
other  human  embryos  ranging  from  27  to 
37  centimetres  [lOf  to  15  inches],  and  up- 
ward, we  have  been  able  to  fix  the  subse- 
quent phases  of  evolution,  not  only  of  the 
temporary  follicles,  but  also  those  of  the 
permanent  teeth.  These  successive  studies 
have  thus  brought  us  up  to,  and  even  be- 
yond, the  period  of  birth.  In  this  manner 
we  have  been  enabled  to  establish  two 
points  which  remained  to  be  elucidated  in 
this  order  of  researches,  namely :  the  mode 
and  epoch  of  the  evolution  of  the  follicles 
of  the  second  and  third  permanent  molars. 
The  results  to  which  we  have  arrived  in 
regard  to  these,  are  the  following :  On  ex- 
amining sections  taken  from  the  jaws  of 
subjects  two  or  three  months  after  birth, 
we  discover  in  the  region  occupied  by  the 
follicle  of  the  first  permanent  molar,  a  pro- 

*  See  Robin  et  Magitot,  loc.  cit.,  p.  75. 


OF    THE    DENTAL    FOLLICLE.  I  •)  i 

vc><  or  prolongation,  cylindrical  in  form, 
emanating  from  the  epithelial  cord  of  the 
latter  follicle,  and  which  takes  a  horizontal 
and  backward  direction,  terminating  in  a 
bullions  extremity.  This  prolongation  is 
the  commencement  of  the  follicle  of  the 
second  permanent  molar.  Thus  we  fix  the 
date  of  the  origin  of  this  follicle  at  the 
third  month  after  birth.  At  about  the 
third  year  of  infancy  the  epithelial  bour- 
geon that  represents  the  enamel-organ  of 
the  third  molar  originates  from  the  cord  of 
the  preceding  tooth,  that  is,  the  second  per- 
niaiicnt  molar.  According  to  the  numerous 
observations  we  have  made,  this  date  may 
lie  regarded  as  very  nearly  accurate,  though 
tin'  difficulties  of  which  we  have  already 
spoken  have  prevented  us  from  following 
out  the  successive  phases  of  evolution  in  a 
very  rigid  manner.  Yet  that  a  little  cap 
of  dentine  is  visible  in  this  follicle  about 
the  twelfth  year.  is  true  beyond  a  doubt. 
Without   continuing    further    the    long 


158  THE    ORIGIN    AND    FORMATION 

analysis  of  the  many  anatomical  prepara- 
tions we  have  made,  we  will  present  a  sum-' 
mary  of  them  all  in  a  tabular  form.  In 
this  are  indicated  the  age  and  size  of  vari- 
ous embryos  corresponding  with  the  suc- 
cessive phases  of  follicular  evolution.  This 
table  is  the  first  which  has  yet  appeared 
giving  these  in  such  a  complete  and  exact 
manner. 

An  examination  of  this  table  enables  one 
to  see  at  a  glance  the  different  phases  of 
dental  evolution  in  man.  The  indications 
which  it  furnishes  are  founded  on  the  ex- 
amination of  a  considerable  number  of  sec- 
tions ;  and  consequently  they  appear  to  us 
to  show  great  accuracy.  Aside  from  their 
physiological  interest,  they  not  only  have 
an  important  bearing  upon  the  complex 
teratology  of  the  dental  system,  but  are 
especially  valuable  in  a  surgical  point  of 
view.  There  will  be  found,  in  fact,  some 
valuable  data  concerning  certain  anomalies, 
whether  in  the  position,  direction,  or  in  the 


OF   THE    DENTAL    FOLLICLE.  159 

different  arrangements  of  the  dental  system. 
Besides  they  throw  Ligh.1  upon  the  pathog- 
ony  of  certain  follicular  cysts  and  help  to 
fix  the  period  at  which  these  pathological 
productions  make  their  appearance,  as  well 
as  thai  of  certain  derangements  of  nutri- 

■ 

tion, —  the  odontomes,  for  example.  We 
believe,  then,  that  it  will  be  found  service- 
able in  certain  cases  in  practice. 

The  results  of  the  observations  we  have 
made  -on  other  species  of  mammals  have 
been  less  conclusive;  sometimes  on  account 
of  the  head  only  being  placed  at  our  dis- 
posal, and  sometimes  owing  to  the  change 
of  size  and  form  that  they  have  experienced 
bj  prolonged  maceration;  and  finally  in 
consequence  of  the  absence  of  all  statistics 
establishing  the  coiTespondence  between 
the  age  and  length  of  the  animal.  Cer- 
tain of  them  have,  however,  enabled  us  to 
gather  some  useful  data  which  we  will 
here  present. 


160 


THE    ORIGIN    AND    FORMATION 


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OF    THE    DENTAL    FOLLICLE.  1  6  1 

Iii  the  canine  species  our  observations 
have  been  limited  to  the  examination  of  a 
lew  Dew-bora  puppies;  accordingly  the 
Pacts  concerning  the  chronology  of  the 
dental  follicle  in  this  animal  are  very  few. 
We  have,  however,  ascertained,  that  at  the 
period  of  birth,  the  follicles  of  the  first 
dentition  are  already  provided  with  a  cap 
of  dentine;  that  the  cord  of  the  permanent 
incisors  has  made  its  appearance,  and  that 
in  l he  centrals  we  can  already  discern  the 
first  traces  of  the  dental  bulbs.  In  the 
ovine  and  bovine  species  our  studies  have 
extended  to  a  large  Dumber  of  embryos,  but 
owing  to  the  absence  of  information  we 
have  not  been  able  to  determine  their  exact 
ages.  We  proceed,  however,  to  give  some 
of  our  observations,  taking  into  considera- 
tion simply  the  length  of  the  animals  ex- 
amined. In  an  ovine  embryo  of  4l}  milli- 
metres |  about  1  v  inches]  in  length  (Figs, 
16  and  1 (.),  Summary  of  Flhts.}  we  find 
on  the  edge  of  the  jaws  only  the  bourrelet, 


162  THE    ORIGIN    AND    FORMATION 

or  projecting  band,  with  no  trace  of  the 
epithelial  lamina.  But  when  the  embryo 
has  attained  52  millimetres  [2  inches]  we 
perceive  the  epithelial  lamina  well  devel- 
oped. (Figs.  17  and  18,  Summary  of  lllus.) 
In  an  embryo  of  65  millimetres  no  addi- 
tional change  is  percejrtible  in  the  develop- 
ment ;  yet  with  a  magnifying  power  of  about 
300  diameters  one  can  study  in  this  the  con- 
stituent elements  of  the  lamina.  (Fig.  18, 
Summary  of  -Illus.) 

When  the  embryo  has  attained  72  mil- 
limetres [about  3  inches]  the  extremity  of 
the  lamina  shows  a  very  marked  enlarge- 
ment, which  represents  the  enamel-organ  of 
the  future  tooth.     (Fig  21,  Gr,    Summary?) 

Ajb  a  little  more  advanced  period,  in  an 
embryo  measuring  82  millimetres  [31 
inches],  the  enamel-organ  and  the  dentine- 
bulb  have  completed  their  formation,  and 
the  follicular  wall  has  made  its  appearance 
at  the  base  of  the  bulb.  (Figs.  26  and  28, 
Summary?) 


OF    THE    DENTAL    FOLLICLE.  I  63 

When  the  embryo  has  attained  1 1  \  cen- 
timetres 1 4.1  inches]  we  observe  thai  the 
walls  arc  completed,  ami  closed  around  the 
epithelial  cord  which  is  about  to  be  rup- 
tured. At  this  period,  also,  we  discover 
the  first  appearance  of  the  dentinecap. 
Such  arc  the  tacts  wc  have  collected  from 
the  embryonal  Lambs  which  we  have  been 
able  to  procure. 

In  the  bovine  embryo  our  observation-, 
in  a  chronological  point  of  view,  have  been 
much  more  limited,  the  head-  only  of  these 
embryos  having  been  placed  at  our  dis- 
posal, without  any  information  as  to  the 
period  of  gestation.  These  specimens,  how- 
ever, have  enabled  us  to  furnish  some  de- 
scriptive details  which  are  very  distinctly 
shown  in  this  animal.  (  Pigs.  38,  41  and  42, 
Summary.)  We  will  state,  however,  that  in 
a  foetus  of  eighl  months  we  have  found  the 
temporary  incisor  teeth  quite  fully  devel 
oped,  the  follicle  of  the  permanent  incisors 
complete,  ami  the  dentine-cap  beginning  to 
form. 


164  THE    ORIGIN    AND    FORMATION 

Our  observations  have  been  made  upon 
equine  embryos  of  different  ages.  From 
these  we  have  determined  certain  facts  in 
relation  to  the  various  phases  of  follicular 
evolution.  For  the  first  three  embryos  we 
are  indebted  to  the  courtesy  of  M.  Raynal, 
of  the  veterinary  school  at  Alfort.  In  the 
youngest  of  these  (14  weeks)  the  enamel- 
organ  of  the  central  nippers  (incisors)  are 
already  formed,  and  the  bulb  has  made  its 
appearance.  For  the  lateral  nippers  the 
enamel-organ  is  just  beginning  to  show  it- 
self. These  facts  indicate  that  the  evolu- 
tion of  the  follicles  varies  in  point  of  time  in 
the  different  incisors;  whereas  the  evolu- 
tion of  the  follicles  of  these  teeth  in  man 
and  other  mammals  appeal's  to  be  synchro- 
nous. For  the  molars,  it  is  found  that  at 
this  same  epoch  the  bulb  has  appeared  for 
all  the  follicles  of  the  first  dentition,  as  have 
also  the  first  traces  of  the  follicular  wall. 

In  a  second  embryo  (of  27  weeks)  the 
follicles  of  the  central  incisors  are  closed, 


OF    THE    DENTAL    FOLLICLE.  165 

while  those  of  the  firsi  lateral  incisors  are 
jusl  beginning  to  exhibit  the  l>nll>s;  and 
those  of  the  second  lateral  incisors  only  the 
enamel-organ.  These  facts,  as  we  see,  ad- 
ditionally confirm  the  unequal  development 
of  the  different  incisors  in  this  animal.  In 
the  molars  the  facts  are  analogous;  the  fol- 
licle of  the  first  temporary  molar  is  closed 
at  this  date,  while  the  enamel-organ  of  the 
second  lias  only  just  made  its  appearance, 
and  no  trace  of  that  of  the  third  molar  is  yet 
visible.  It  is  at  this  period,  also,  that  the 
first  indication  of  the  enamel-organ  appears 
for  the  first  permanent  molar. 

In  a  third  embryo,  measuring  255  mil- 
limetres [10  inches  |,  corresponding  to  about 
28.1  weeks,  the  follicles  of  the  permanent  in- 
cisors are  closed  and  complete;  the  enamel- 
organ  is  well  developed.  The  ameloblasts 
of  the  interior  bed  are  verj  large,  and  the 
external  epithelial  layer  has  already  disap- 
peared,* bul  no  t  race  of  dentine  yet  appears. 

*  [The  above  statement,  concerning  the  early  disappear- 
ance of  the  external  epithelial  layer  of  the  enamel-organ,  is 


1(t6       ♦  THE    ORIGIN    AND    FORMATION 

The  follicles  of  the  permanent  incisors 
have  arrived  at  the  period  when  the  enamel- 
organ  already  caps  the  bulb,  which  is  just 
appearing,  but  is  not  yet  constricted  at  its 
base.  (Fig.  29,  K,  Summary.}  For  the  tem- 
porary molars  the  follicles  are  about  equal- 
ly developed.  They  are  closed  and  well 
formed,  but  without  any  appearance  of  the 
dentine-cap.  The  organ  of  coronal  cement 
is  already  beginning  to  manifest  itself. 
From  the  fragments  of  the  ruptured  epi- 
thelial cord  numerous  buddings  have  been 
produced. 

From  the  fourth  (an  equine  foetus  of  31^ 
weeks),  owing  to  a  very  prolonged  macera- 
tion in  alcohol,  we  were  prevented  from  de- 
riving much  advantage.  We  were  only 
able  to  determine  that  the  temporary  folli- 
cles were  fully  developed  and  provided  with 
caps  of  dentine  of  considerable  thickness. 
Some  fragments  of  the  epithelial  cord  (long 
since  broken,  without  doubt,)  were  still  re- 

evi den tly  erroneous ;  the  sections  examined  which  led  to  this 
opinion  were  probably  defective. — Tr.]  * 


OF    THE    DENTAL    FOLLICLE.  1  <»7 

maining.  The  organ  of  corona]  cement  was 
fully  developed. 

We  will  conclude  these  chronological  con- 
siderations with  a  few  notes  relative  t<»  the 
rodents:  In  an  embryonal  guinea-pig  of  2 
centimetres  |  J  inch]  in  total  Length,  which 
appeared  to  correspond  to  about  the  middle 
period  of  gestation,  the  follicle  was  at  the 
stage  when  the  enamel-organ,  in  form  of  a 
hood,  covers  the  bulb;  there  was  no  follicu- 
lar wall  or  dentine-cap  apparent. 

In  another  embryo  of  the  same  species, 
of  4  centimetres  |  1 1  inches]  in  length,  the 
temporary  follicles  were  formed,  and  their 
stages  of  development  were  nearly  the  same. 
They  were  provided  with  a  dentine-cap, 
covered  with  a  thin  layer  of  enamel.  In  the 
rabbit  we  discover  that,  at  birth,  the  incisors 
have  effected  their  eruption, the  molar-  -till 
enclosed,  but  already  capped  with  thick 
layer-  of  dentine  and  enamel.  Beneath  the 
temporary  molars  we  observe  the  presence 
of  the  permanent  follicles,  already  provided 


168  THE    ORIGIN    AND     FORMATION 

with  a  thin  but  distinctly  manifest  layer  of 
dentine. 

We  will  not  pursue  these  considerations 
further,  which  are  of  less  interest  in  the 
lower  mammals  than  in  man,  in  regard  to 
whom  we  have  presented  a  large  number 
of  examples. 


OF   THE    DENTAL    FOLLICLE.  1  0'.» 


CHAPTER    VII. 


CBITICISM    OF   THEORIES       l.'IM   Ml".     VXD    CONi   USIONS. 

npiIK  problem  of  the  genesis  and  forma- 
-*-    tion  of  the  dental  follicle  in  mammals 

has,  for  a  loni:  time,  l>een  the  subject  of 
numerous  researches,  and  lias  given  rise  t<> 
many  theories.  The  relatively  early  period 
in  embryonic  lite  at  which  these  phenomena 
commence;  the  difficulties  attending  the 
preparation  of  the  specimens  (the  treat- 
ment by  different  reagents  to  which  they 
must  be  submitted,  etc.),  are  so  many  causes 

which  have   retarded   the  progress  of  exact 

knowledge  regarding  the  embryogenic  evo- 
lution  of  these  organs.  The  question  has 
passed  through  numerous  phases,  and,  with- 
out going  l>aek  very  far  in  its  history,  and 
without  presenting  the  opinions  of  ancienl 
authors,  imbued  with  preconceived  notions 

12 


170  THE    ORIGIN    AND    FORMATION 

of  the  nature  of  the  teeth,  or  strangers  to 
the  processes  of  investigation  of  the  modern 
anatomical -school,  we  will  say  that  in  going 
back  no  farther  than  the  middle  of  the  last 
century  we  find  that  Herissant*  having  con- 
ceived that  he  found  on  the  surface  of  the 
mucous  membrane  of  the  gums  certain  small 
depressions,  considered  them  to  be  orifices 
of  canals  communicating  with  the  dental 
follicles.  This  opinion,  which  rested  on  no 
anatomical  fact,  was  adopted  by  only  a 
few  authors  (Bonn,  1773;  Oudet,  1835). 
According  to  the  theory  of  Herissant, 
which  we  find  at  a  later  day  more  clearly 
presented  by  Groodsir,  the  mucous  mem- 
brane of  the  gums  would  be  the  point  of 
origin  of  the  follicle,  the  wall  of  which 
would  be  developed  before  the  follicle  it- 
self.     In   1835,f    in    an   important    work, 

*  Nouvelles  recherches  sur  la  formation  de  V email  des 
dents  et  sur  celle  des  gencives.  Mem.  de  VAcad.  Paris, 
1754. 

f  Meletemata  circa  dentium  mammalium  evolutione  Vratis- 
larice.     In.  4°,  1835,  p.  12. 


OF    THE    DENTAL    FOLLK  LE.  171 

Rasdikow  advanced  tin-  theory  that  the 
dental  follicle  is  produced  al  the  inner  face 
of  the  mucous  membrane,  without  the- nec- 
essary participation  of  the  latter;  however, 
he  does  not  specify  which  of  the  organs  of 
the  follicle  appeals  first,  nor  how  the  others 
are  produced.  Nevertheless,  Henle,*  Bis- 
choff,f  and  KollikerJ  (in  the  first  edition 
of  his  microscopical  anatomy)  support  his 
opinion.  A  few  years  later  appeared  the 
work  of  Goodsir,§  in  which  is  formulated 
that  well-known  theory  according  to  which 
both  the  temporary  and  the  permanent  fol- 
licles originate  directly  from  the  mucous 
membrane  itself.  Immediately  adopted, 
without  verification  by  the  majority  of  au- 
thors, it  is  even  now  nearly  the  only  theory 
found  in  the  greater  number  of  treatises  on 

*Anat.  i/i'ii.  1845,  p.  Hi  <t  suiv. 

t  TraiU  du  developpement,  1845,  p.  401-418. 

\Mikro8cop.  Aunt..  1856,  traduction  franchise  dt  beclard 
<  i  Se\ .  p.  490. 

£  On  tin-  origin  and  development  oj  thi  pulp  and  sacs  of 
the  human  teeth.  Edinburgh  "  Medical  and  Surgical  Jour- 
nal," 1838. 


172  THE    ORIGIN    AND    FORMATION 

anatomy  and  physiology.  We  will  not 
describe  here  this  theory,  according  to  which 
the  follicles  of  the  two  dentitions  result 
from  a  simple  introversion  of  the  mucous 
membrane ;  it  is  founded  on  no  anatomical 
fact,  unless  it  be  the  formation  of  a  groove 
which  is  produced  on  the  alveolar  border 
of  the  embryo  by  a  prolonged  maceration 
of  the  preparations,  thus  effecting  the  sepa- 
ration of  the  epidermic  bed,  which  forms 
the  epithelial  band,  from  the  groove  which 
incloses  it.  It  is,  then,  as  we  have  said, 
solely  by  an  artificial  process,  as  Kolliker* 
and  Kollmann  f  have  already  remarked, 
that  the  theory  in  question  can  have  any 
appearance  of  reality;  for  nothing  in  the 
normal  condition  of  the  jaws  can  be  found 
to  lend  support  to  it  in  any  way.  Not- 
withstanding the  success  of  Groodsir's  the- 
ory, universally  accepted  in  England  and 
Germany,  N.  Guillot  published  in  France 

*Histologique  humaine.     Edit.  Trad.  fran<?aise,  1869. 
f  Loc.  cit.,  p.  150. 


OF    THE    l>i  via  I.    FOLLICLE.  I  To 

a  work*  in  which  he  endeavored  t<>  show 
thai  the  teeth  are  developed  without  the 
slightest  participation  of  the  mucous  mem- 
brane; that  it  is  from  a  mass  originating  in 
tlic  depth  of  the  embryonal  tissue  that  the 
follicle  is  produced.  This  mass  he  calls 
the  i  nit  ml  spheroid,  or  primitive  trace  of 
the  tooth,  lie  describes  in  this  "  spheroid  " 
thre<'  divisions:  a  central  one.  which  he 
names  the  nnch-ns.  representing'  the  bulb  ,' 
an  intermediate  one  surrounding  the  other, 
the  < ma/niel-orga/n  ;  and  lastly,  the  external 
one,  which  will  become  organized  to  form  a 
membrane,  he  calls  the  dental  sac.  From 
this  description,  as  a  whole,  it  is  easy  to  see 
that  N.  Gruillot  has  limited  himself  to  the 
examination  and  figuring  of  sections  made 
through  follicles  which  are  in  an  advanced 
stage  of  evolution,  and  that  he  has  not  hit 
upon  the  mode  of  origin  of  the  component 
parts   <>f   the   organ    and    their   successive 

*  Recherche*  sur  In  genise  >-t  V evolution  dee  dents  ft  des 

Mdchoirea.      Ann.  des  8C.  nut.,  IV"  sc'rii',  t.   IX,  1858. 


174  THE    ORIGIN    AND    FORMATION 

phases  of  development.      This  work,  then, 
has  thrown  no  light  upon  the  question. 

Several  years  later  (in  1860)  appeared 
in  France  an  extended  work,  published  by 
M.  Ch.  Robin,  in  connection  with  one  of 
the  authors  of  this  work.*  This  memoir 
contained  a  complete  theory  of  follicular 
evolution,  according  to  which  the  dental 
bulb  is  the  first  part  of  the  follicle  that 
appears  in  the  depth  of  the  jaws,  at  the 
bottom  of  the  groove  and  in  the  vicinity  of 
the  principal  vessels  and  nerves ;  afterward 
the  enamel-organ  is  seen ;  and  then  the  wall 
emanating  from  the  bulb,  and  rising  upon 
the  sides  of  these  organs  so  as  to  surround 
them  and  to  unite  at  the  apex  of  the  folli- 
cle. Whatever  may  be  the  accuracy  of  the 
descriptions  in  this  work,  it  is  evident  that 
its  authors  misconceived  the  true  order  of 
the  genesis  of  the  follicle  ;  for  in  reality  the 
enamel-organ  makes  its  appearance  before 
the  bulb. 

*  Robin  et  Magitot,  M6tnoire  cit<5  Journal  de  physiologie 
de  Brown-Sequard,  1860-61. 


OF    THE    DENTAL    FOLLICLE.  1 75 

Whence  comes  this  error  in  the  interpre- 
tation of  the  very  first  phenomena  of  folli- 
cular evolution?  It  results  evidently  from 
the  too  exclusive  mode  of  examination 
which  was  adopted;  for  the  observations 
were  made  upon  preparations  of  follicles 
gradually  flattened  between  two  plates  of 
glass.  Very  few  sections  were  made.  The 
authors  wished  thereby  to  preserve,  in  their 
reciprocal  relations  all  the  parts  which  they 
dissected,  for  the  purpose  of  further  re- 
searches in  detail.  The  fear  of  deforming 
the  sections  and  disturbing  the  relations 
which  sometimes  result  from  cuttings  made 
upon  masses  of  tissues  somewhat  thick, 
and  we  must  say  the  insufficiency  of  the 
processes  of  hardening  known  at  that 
period, —  all  these  combined  singularly  to 
Lead  these  anatomists  into  the  error  that 
they  have  there  committed. 

The  question  was  at  this  point,  wheo 
Kolliker  discovered  (1863*)  the  existence 

*  Die  Enttoicklung  der  Zahnsdckchen  der  Wiederk&uer. 

Zeitschr.  f.  Wissen.  Zool.  18G3.     Gewebelehre,  4  Aufl. 


176  THE    ORIGIN    AND    FORMATION 

of  an  epithelial  band  subjacent  to  the  gin- 
gival ridge  of  the  mucous  membrane,  and 
which  extends  the  entire  length  of  the 
jaws.  This  continuous  lamina  Kolliker 
calls  the  enamel-organ;  but  we  regard  it 
only  as  a  simple  dependence  of  the  epithe- 
lial band.  The  term  enamel-organ  does  not 
appear  to  us  to  be  appropriate  to  a  lamina 
which  does  not  contribute  directly  to  the 
formation  of  the  follicle,  since  it  is  upon  a 
certain  number  of  points  of  this  that  bour- 
geons appear,  from  which  the  enamel-organs 
are  directly  developed.  These  bourgeons 
are  in  number  equal  to  that  of  the  future 
teeth;  and  in  the  intervals  between  the 
bourgeons,  or  enamel-organs,  the  epithelial 
lamina  remains  unchanged. 

Whatever  may  be  said  of  the  interpreta- 
tion of  them,  the  views  of  Kolliker  are  very 
just ;  and  they  became  the  starting-point  of 
a  series  of  observations  which  gave  to  the 
question  of  the  evolution  of  the  dental  fol- 
licle  an  entirely  new   aspect.      Two  facts 


OF    THE    DENTAL    FOLLICLE.  177 

were  from  that  time  settled,  namely,  that 
the  enamel-organ  appears  as  the  firsl  con- 
stituent part  of  the  follicle,  and  that  its 
origin  is  epithelial.  Upon  this  last  poinl 
tin-  views  previously  pur  forth  by  Marcuses 
and  Huxley  were  continued."  Following 
the  work  of  Kolliker  are  grouped  a  consid- 
erable number  of  researches  emanating  from 
his  pupils,  or  coining  from  other  German 
schools.  Such  are  the  memoires  of  Wal- 
deyer,  Hertz,  Wendzel,  Kollmann,  etc.  f 

*  Marcusen,  Ueber  die  Entwicklung  der  Z&hne.  Bulletin 
de  VAcad.  imperiale  de  Saint  Petersbourg,  1849.  Huxley, 
Quint.  Journal  of  Microscopical  Science,  1854,  1855.  1857. 

fWaldeyer,  Untersuch.  uber  die  Entwicklung  der  Z&hne: 
I  Abth.  Konigsberg  und  Jahrbttcher  IV.  Bd.  1864;  II  Abth. 
Zeitschr.  fur  rat.  Med.;  Ill,  24  Bd.  1865.— IV.  Bau  und 
Entwicklung  der  Z&hne  in  Strieker,  Handbuch  der  Lehre 
ton  den  Gewehen.  Leipzig,  1871,  p.  333  et  Buiv.— Hertz, 
Untersuchungen  uberfeineren  Ban  und  die  Entwicklung  der 
Z&hne.  Virch.  Arch.  1866,  Bd.  37;  id.,  Kin  Full  von 
geheiUer  Zahnfractur  mit  nachfolgender  Schnielzbildunff. 
Virch.  Arch.  1806.  2*  Bd. — Wendzel,  Untersuchungen  fiber 
das  Schtnehorgan  und  den  Schnieh.  etc.  Arch,  von  ILkde. 
1868,  p.  97.— Kollmann,  Entwicklung  der  Milch  und  Ersatz- 
z&hne  beim  Menschen.  Zeitschrifl  fur  Wissenschaftliche 
Zoologie,  von  Seibold  und  KSlliker;  Zwanzigster  Baud. 
Zweitea  Heft.  p.  145.     Leipzig,  1870. 


178  THE    ORIGIN    AND    FORMATION 

In  these  different  works  the  idea  of 
Kolliker  is  taken  at  the  initial  point.  Wal- 
deyer  described  exactly  the  descent  of  the 
cord,  and  the  formation  of  the  component 
parts  of  the  follicle.  He  indicates,  also,  that 
the  follicles  of  the  permanent  teeth  arise 
from  buddings  from  the  primitive  cords; 
but  he  fails  to  mention,  in  regard  to  them, 
the  different  modes  of  genesis,  and  also  the 
precise  points  where  this  genesis  takes  place. 
He  points  out,  moreover,  in  his  last  publica- 
tion,* the  unsettled  difficulties  which  exist 
in  these  questions,  notwithstanding  the  nu- 
merous works  published  upon  this  subject. 
Hertz  and  Wendel  support  the  opinions 
promulgated  by  Kolliker  and  Waldeyer, 
without  adding  anything  new  to  the  ques- 
tion of  the  origin  of  the  follicle.  They 
have,  however,  advanced  some  new  ideas 
upon  other  points  of  follicular  evolution, 
which  we  will  discuss  on  another  occasion. 
As  to  Kollmann,  the  last  German  anato- 

*See  in  Strieker,  loc.  cit.  1871,  p.  352  (English  Edition). 


01      I  Hi:    DENTAL    I  oi.i.it  1.1  .  1  79 

mist  who  has  studied  the  question,  lit-  adopts 
unhesitatingly  the  views  of  Kolliker  ;m<l 
Waldeyer  od  the  subjeci  of  the  origin  of 
the  enamel-organ  of  the  temporary  teeth; 
but  in  regard  to  the  origin  of  the  perma- 
nent follicle,  sometimes  he  derives  it  direct- 
ly from  the  mucous  membrane,  sometimes 
from  the  epithelial  debris  of  the  primitive 
cord,  and  at  others  from  an  epidermic  glob- 
ule. It  is  also  from  one  of  these  last  that 
he  makes  the  supernumerary  follicles  arise, 
as  we  have  already  mentioned.""  The  Ger- 
man authors  are,  then,  very  far  from  agree- 
ing:, ^ls  we  S(J<",  in  regard  to  the  mode  of 
origin  of  the  dental  follicle.  As  to  the 
phenomena  which  take  place  within  that 
organ  after  the  origin  of  the  bulb,  and  the 
formation  of  the  wall,  and  the  transforma- 
tion of  the  enamel-organ,  they  are  <\\\  in 
controversy.  In  our  opinion,  and  we  may 
thus  in  a  few  word-  resume  our  work,  the 
formation  of  the  dental  follicle  consists,  es- 

*  [See  p.  66  of  this  work—  Tk.] 


180  THE    ORIGIN    AND    FORMATION 

sentially,  in  the  genesis  of  two  organs,  one 
of  which  is  of  an  epithelial  nature,  ema- 
nating from  the  epithelium  of  the  mucous 
membrane,  the  other  of  an  embryoplastic 
nature,  originatino;  m  the  midst  of  the  em- 
bryonic  tissue  of  the  jaws.  The  first  of 
these  is  the  enamel-organ,  the  second  is  the 
bulb,  or  dentine-organ ;  thus  they  are  formed 
individually  and  then  proceed  to  meet  each 
other.  The  enamel-organ  becomes  in  a  man- 
ner the  cap  of  the  bulb,  while  from  the 
base  of  the  latter  emanate  membranous 
processes,  which  envelop  little  by  little  the 
two  organs,  and  at  last  entirely  close  the 
follicle.  If  one  examines  the  origin  and 
growth  of  these  organs  from  the  point  of 
view  of  general  physiology,  he  is  immedi- 
ately struck  with  the  extreme  analogy  they 
present  to  the  phenomena  of  the  formation 
of  the  hair-follicles.  In  the  latter,  as  well 
as  in  the  former,  one  sees  on  the  one  hand 
an  epithelial  cord  which  descends  from  the 
Malpighian  layer  into  the  dermis ;  then  on  a 


OF    THE    DENTAL    FOLLICLE.  181 

point  of  the  latter  appears  the  bulb,  which 
penetrates  the  former,  ami  makes  of  it  a 
Cap  for  itself;  while  from  its  base  emanate 
those  processes  which  are  to  form  the  walls 
of  the  follicle.  These  facts  show  the  close 
analogy  of  these  two  organs.     (Fig.  40.) 

Thus  we  mid  confirmed,  by  actual  physi- 
ological ami  embryological  facts,  the  theory 
enunciated  a  Long  time  since  by  De  Blain- 
ville,  regarding  the  analogy  in  the  compo- 
sition and  formation  of  the  plianeres,  as  well 
as  the  doctrine  of  the  j>/-o<///rfs  developed 
with  so  much  precision  in  the  modern  ana- 
tomical school  of  Ch.  Robin. 

CONCLUSIONS. 

1st.  The  dental  follicles  first  appear  as  a 
cord  emanating  from  the  epithelial  layer  of 
the  oral  mucous  membrane. 

2d.  The  cords  that  give  origin  to  the  fol- 
licles  of  the  first  dentition  arise  directly 
from  a  process  of  the  oral  epithelium  (epi- 


182  THE    OEIGIN    AND    FORMATION 

thelial  band  and  epithelial  lamina).  The 
cords  for  those  permanent  teeth  which  .suc- 
ceed the  temporary  ones  are  diverticula  or 
outgrowths  from  the  primitive  cords.  As 
for  the  cords  of  the  other  permanent  teeth, 
those  for  the  first  molars  originate  directly 
from  the  epithelium  of  the  mucous  mem- 
brane, and  the  remaining  ones  (eight  in 
number)  from  the  cords  of  the  preceding 
molars.     (See  table.) 

3d.  The  cord,  whatever  may  be  its  point 
of  origin,  is  invariably  epithelial ;  it  is  com- 
posed outwardly  of  a  layer  of  prismatic 
elements  of  the  Malpighian  stratum,  and  in 
the  interior,  of  polyhedric  epithelial  cells. 

4th.  The  extremity  of  the  cord,  which 
soon  takes  the  form  of  a  club-shaped  swell- 
ing, constitutes  the  enamel-organ  of  the 
future  follicle. 

5th.  The  dental  bulb  apj3ears  spontane- 
ously in  the  midst  of  the  embryonic  tissue 
and  at  a  point  in  immediate  proximity  to 
the  deeper  face  of  the  enamel-organ. 


OF   THE    DENTAL    FOLLICLE.  Is"' 

6th.  The  enamel-organ  covers  the  bulb, 
serving  as  a  cap  for  it;  an  arrangement 
which  continues  during  all  the  periods  of 
evolution,  preceding  the  formation  of  the 
dentine  and  the  enamel. 

7th.  The  follicular  processes  emanate 
directly  from  the  elements  of  the  bulb,  and 
rise  from  its  base  to  the  summit  of  the  fol- 
licle, where  they  unite  and  constitute  the 
follicular  sac. 

8th.  Synchronous  with  the  closing  of  the 
follicles  is  the  rupture  of  the  cord;  and 
from  this  period  the  follicle  loses  all  con- 
nection with  the  epithelium  of  the  mucous 
meml  irane.  The  formation  of  the  follicle  is 
now  complete. 

9th.  The  evolutionary  phenomena  of  the 
follicles  in  both  dentitions  are  identical  as 
to  their  nature;  the  only  perceptible  differ- 
ences are  in  regard  to  the  exact  point  from 
which  the  epithelial  cords  originate,  and 
the  length  of  time  necessary  to  accomplish 
their  successive  phases  of  evolution. 


184  THE    DENTAL    FOLLICLE. 

10th.  The  mode  of  evolution  of  the  den- 
tal follicle  and  of  the  pileous  follicle  is 
identical. 

Frank  :  Are,  then,  our  readings  to  terminate 
here  ? 

Teacher  :  The  appearance  of  the  second  me- 
moir in  the  series  has  been  long  delayed,  owing 
to  the  death  of  one  of  its  authors,  the  lamented 
Dr.  Ch.  Legros.  Much  of  the  materials  for  this, 
I  am  informed,  had  been  collected  before  his 
decease ;  but  the  preoccupation  of  Dr.  Magitot 
has  prevented  his  completing  it  up  to  the  pres- 
ent time.  I  am,  however,  daily  expecting  the 
arrival  of  this  treatise,  and,  should  it  be  found 
desirable,  we  may  resume  our  readings. 

If  you  have  obtained  a  clear  idea  of  the  phe- 
nomena of  the  origin  and  growth  of  the  dental 
follicle  from  the  present  work,  you  have  acquired 
far  more  than  has  been  hitherto  taught  in  any 
of  our  medical  or  dental  schools,  or  can  be  found 
in  any  other  publication  upon  this  subject ;  and 
though  it  will,  doubtless,  become  necessary  for 
you  to  modify  your  views  in  some  particulars,  as 
this  branch  of  science  progresses,  yet  the  knowl- 
edge you  have  here  gained  will  enable  you  to 
readily  perceive  and  appreciate  the  value  of 
future  researches  made  either  by  yourselves  or 
by  other  observers  in  this  field  of  study. 


SUMMARY  OK  ILLUSTRATIONS 


AND    A    BRIEF 


DESCRIPTIVE   REVIEW. 


All  figures  not  accredited  to  other  sources  are  copied 
from  the  original  work. 

The  dental  bulbs,  in  some  of  the  following  figures,  pre- 
sent a  vascular  appearance,  not  seen  in  those  from  which 
they  are  copied.  It  was  believed  that  by  thus  representing 
them,  the  student  might  more  readily  recognize  the  diff- 
erent parts  of  the  developing  follicle. 


13 


186  SUMMARY. 

Fig.  1. — This  diagram  shows  the  relative  position  of  the 
different  layers  which  are  designated  the  mucous,  or  "prop- 
er "  mucous,  membrane  by  various  writers.  The  column  on 
the  left  gives  the  names  and  location  of  the  strata  of  the 
mucous  membrane  as  we  think  they  should  be  designated. 
The  horizontal  lines  show  the  relative  location  of  these  lay- 
ers, without  any  regard  to  their  thickness.  M.  S.  D.,  del. 
(See  p.  11.) 

Fig.  2. — This  cut  was  designed  to  illustrate  the  cells  of 
the  epidermis  E,m  some  of  their  various  phases,  as  de- 
scribed (p.  18  et  seq.)  a,  Stratum  corneum;  b,  stratum  Mal- 
pighii,  with  its  prismatic  or  columnar  layer  resting  upon  the 
basement  membrane,  b  m;  c,  upper  portion  of  the  dermis. 
The  papillae  are  not  represented  in  this  figure,  nor  the  sub- 
dermal  layer.     M.  S.  D.,  del.     (See  p.  18  et  seq.) 

Fig.  3. — The  so-called  "spinous,"  "ridged,"  "imbri- 
cated," "  aculeated,"  "  prickle  "  or  "  heckle  "  cells.  Frey. 
(See  p.  50.) 

Fig.  4. — Showing  the  lowest  layer  of  the  Malpighian 
stratum  (a);  the  intermediate  matter  (&);  the  basement 
membrane  (c);  and  the  fibrous  tissue  of  the  dermis  {d). 
(From  Frey.  Diagrammatic.)  Though  the  cells  of  this 
layer  always  stand  nearly  perpendicularly,  their  form  is 
varied;  for  example,  the  basal  extremities  are  truncated  in 
the  ameloblasts,  somewhat  like  those  seen  in  Fig.  7,  p.  191. 
(See  p.  21.) 

Fig.  5. —  Stellate  cells,  such  as  compose  the  "stellate 
reticulum"  of  the  enamel-organ.  Diagrammatic,  from 
Frey.     (See  p.  77.) 

Fig.  6. — Cut  to  represent  the  basal  aspect  of  a  layer  of 
ameloblasts;  showing  their  prismatic  or  hexagonal  form. 
M.  S.  D.,  del.    (See  p.  85.) 


I'm..   1. 

1-1  Class.      2d  Class.      8d  Class.    1th  Class. 


BO 

a 

t 
2 
a 
H 

Strat.  corn. 

Mi 

Stral  Malp. 

•M.  nierab. 

- 

z 

- 

Basement  memb. 

M.  memb. 

Dermis-*  ;■"-''•■"'■ 
|  Pars  ret. 

M.  memb. 

3 

- 
= 

Subdermis. 

— 

Fig.  2. 


Pis.  3. 


Pig.  5. 


ppsr^ 


Fie.   i. 


Pig.  6. 


188  SUMMAET. 

Fig.  9. — Meckel's  cartilage  ;  from  a  human  embryo  of 
forty  to  forty-two  days.     (Magnified  25  diam.) 

a,  Enlargement  of  cartilage  near  the  neck  of  the  malleus; 
b,  the  mental  symphysis  where  the  two  homologous  parts 
unite;  m,  head  of  the  malleus;  n,  handle  of  the  same;  e, 
cartilage  of  the  incus;  o,  that  of  the  os  lenticulare;  I,  that 
of  the  stapes.  One  side  of  the  jaw  has  been  outlined  to 
show  the  relative  position  it  will  occupy  when  ossification 
takes  place.  (For  further  description  of  this  and  following 
figures,  see  p.  32  et  seq.)     Magitot  and  Robin. 

Fig.  10. — Cranium  of  a  human  foetus  of  four  months; 
natural  size;  showing  .the  membrane  of  the  tympanum, 
with  the  cartilages  of  the  incus  and  malleus  (&);  also  the 
extra-tympanic  portion  of  Meckel's  cartilage  (a).  Magitot 
and  Robin. 

Fig.  11. — Right  inferior  maxilla  of  a  human  embryo  of 
about  three  months;  natural  size.  Soft  parts  removed  from 
the  internal  face,  showing  relative  position  of  Meckel's  carti- 
lage, a,  Extra- tympanic  portion;  b,  symphysis;  n,  manu- 
brium mallei  (handle  of  hammer);  e,  incus  (or  anvil).  Magi- 
tot and  Robin. 

Fig.  12. — From  a  human  embryo  of  about  sixty  days; 
natural  size.  Soft  parts  removed,  showing  Meckel's  carti- 
lage and  lingual  face  of  the  jaw-bone,  left  side.  In  this  the 
cartilage  has  much  the  appearance  of  a  very  large  bristle. 
A,  Extra- tympanic  part;  b,  symphysis;  n,  malleus.  M .  S.  D., 
del. 

Fig.  13. — From  a  foetus  of  four  months;  showing  the 
palatal  aspect  of  the  inter-maxillary  bones.  M.  S.  D.,  del. 
(See  p.  40.) 


Fig.  9. 


Fig.  11. 


Fig.  10. 


Pig.  12. 


r 


Ki<;.    13. 


190  SUMMARY. 

Fig.  14. — Vertical  section  of  the  anterior  part  of  the  face 
of  a  human  embryo  of  about  45  days,  measuring  3  cen- 
timetres [1%  ml-     (Magnified  80  diam.) 

a,  a,  Meckel's  cartilage;  b,  first  trace  of  the  submax. 
glands;  c,  depression  of  the  mucous  membrane;  a",  epi- 
thelial band,  bourrelet  of  the  lower  jaw  (see  description,  p. 
51  et  seq.)-.  d,  epithelial  band  of  upper  jaw;  E,  section  of 
the  tongue;  F,  F,  F,  F,  oral  cavity,  a  thin  bed  of  epitheli- 
um clothes  its  surface;  g,  upper  jaw;  H,  H,  incisive  (or  in- 
termaxillary) bourgeons,  which  have  already  united  at  the 
median  line. 

This  central  line  does  not  appear  in  the  original  figure, 
and  should  terminate  where  it  enters  the  lighter  part.  (See 
description,  p.  149.) 

Fig.  15. —  Embryo  of  40  days,  showing  the  mouth  and 
palatal  region.     (Coste). 

1,  First  appearance  of  the  nose;  2,  2,  alse  of  the  nose;  3, 
closure  of  the  incisive  processes;  4,  median  portion  of  upper 
lip,  formed  by  the  approach  and  union  of  the  two.  incisive  (or 
intermaxillary)  processes,  the  little  notch  in  the  median 
line  still  indicating  the  primitive  separation  of  the  two 
processes.     (See  p.  29.) 

Fig.  7. — Taken  from  Kolliker's  Manual  of  Hist.,  showing 
"a  simple  papilla  [of  the  mucous  membrane],  with  mani- 
fold vessels  and  epithelium,  from  the  gums  of  an  infant. 
(Magnified  250  diam.)"  It  is  given  here  principally  to  show 
the  cells  of  the  epidermis.     (See  p.  26.) 


Kh.     14. 


Kii..  15. 


Fig.  :. 


S 


192  SUMMARY. 

Fig.  16. — Vertical  section  taken  from  the  incisive  region 
of  an  ovine  embryo,  42  millimetres  [1%  inches]  in  length. 
(Magnified  80  diam.)  a,  Meckel's  cartilage;  c,  depression 
of  mucous  membrane;  d,  epithelial  band.  The  close  prox- 
imity of  the  parts  of  the  severed  cartilage  shows  the  cut  to 
have  been  taken  from  the  anterior  portion  of  the  jaw.  (See 
p.  53.) 

Fig.  17. — Vertical  section  of  the  anterior  portion  of  the 
lower  jaw  of  a,n  ovine  embryo,  59  millimetres  [about  2  inches] 
in  length.  E,  E,  epithelial  lamina,  emanating  from  the  epi- 
thelial band.  The  letters  a,  c,  d  refer  to  the  same  parts  as 
in  the  preceding  figure.     (See  p.  63.) 

Fig.  18. — Vertical  transverse  section  of  the  left  branch  of 
the  lower  jaw  of  an  ovine  embryo,  65  millimetres.  (Magnified 
260  diam .)  This  and  Fig .  17  show  the  arrangement  of  the  ele- 
ments of  the  epithelial  band,  and  also  the  epithelial  lamina. 
d,  Epithelium  of  the  mucous  membrane,  extending  nearly 
vertically  into  the  embryonal  tissue  and  constituting  the 
epithelial  band,  and  the  lateral  process  or  epithelial  lamina. 

E,  Epithelial  lamina,  emanating  from  the  band.  The  band 
and  lamina  are  surrounded  by  the  embryonal  tissue  of  the 
jaw.  This  portion  of  the  engraving  is  faulty,  in  that  the 
nuclear  elements  appear  lighter,  whereas  they  should  be 
darker,  than  the  surrounding  mass.     (See  p.  63  et  seq.) 

Fig.  19. —  From  a  porcine  embryo  (copied  from  Frey). 
d,  Mass  of  epithelium, —  the  "dental  ridge,1'  "maxillary 
rampart "  or  "  kieferwall  ":  b,  younger  layer  of  epithelium; 
c,  deepest  layer, —  the  columnar  or  prismatic  stratum;  e, 
enamel-organ.     (See  p.  52.) 


Fid.  16, 


Kio.  IT.  a 

c 


Fie    1!). 


a  e 

Fig.  IS. 


' 


194 


SUMMARY. 


Fig.  20.— Section  from  an  embryonic  lamb  a  little  older 
than  that  from  which  Fig-.  18  was  taken;  showing  the 
epithelial  lamina.  (Magnified  350  diam.)  c,  Prismatic  or 
columnar  cells,— a  continuation  of  the  lowest  layer  of  the 
Malpighian  stratum;  d,  large  polygonal  cells  of  the  epi- 
thelial band  (bourrelet);  E,  smaller  polygonal  cells  of  the 
epithelial  lamina.  The  lamina  now  presents  an  enlarged 
extremity,  and  this  is  the  rudiment  of  the  enamel-oman 
(See  p.  69.) 

Fig.  21.— From  the  lower  jaw  of  an  ovine  embryo  (left 
side),  measuring  72  millimetres  [2£  inches].  (Magnified  80 
diam.)  d  and  E  same  as  in  preceding  figures;  g,  rudi- 
mental  enamel-organ.     (See  p.  70.) 

Fig.  23.— From  a  bovine  embryo  (Wedl).  d,  Epithelial 
band  ("dental  ridge");  b,  enamel-organ  ("follicular  pro- 
cess"); c,  epithelium  of  the  margin  of  the  under  lip,  with 
rudimentary  hair-follicles.    (Magnified  15  diam.) 

Fig.  24.— From  the  incisive  region  of  an  ovine  embryo, 
lower  jaw,  115  millimetres  [4|  inches].  (Magnified  80  diam.) 
a,  Meckel's  cartilage;  b.  osseous  trabecular;  c,  c,  dental 
artery;  d,  epithelial  band;  E,  epithelial  lamina;  /,  cord;  g, 
enamel-organ;  H,  rudimentary  bulb.  • 

In  this  figure,  which  has  been  drawn  from  nature,  as  well 
as  all  the  others,  certain  defects,  which  have  resulted  from 
too  long  maceration,  have  been  preserved  in  the  drawings;, 
hence  the  space  seen  between  the  follicular  wall  (I)  and  the 
enamel-organ  (g)  is  artificial,  and  does  not  appear  in  fresh 
preparations.  It  will  be  seen,  on  the  right  side  of  the  figure, 
that  the  cut  was  not  in  line  with  the  follicle,  and  that  only 
the  lamina  is  apparent. 


g      E 


Pig.  22. 


'■'     - 


Pig.  28. 


rf  A 


j  --«;-.  i  '-' 


Fig.  24. 


196  SUMMARY. 

Fig-.  25. — From  lower  jaw  of  an  equine  embryo,  190  milli- 
metres [7f  inches]  in  length.     (Magnified  80  cliam.) 

a,  Meckel's  cartilage;  b,  traces  of  ossification;  E,  epi- 
thelial lamina;  F,  cord;  g,  enamel-organ;  H,  bulb;  I, 
follicular  wall.  This  figure  shows  the  same  defect  alluded 
to  in  Fig.  24. 

Fig.  26. — From  lower  jaw  of  an  ovine  embryo,  82  milli- 
metres [3£  inches]  in  length.     (Magnified  80  diam.) 

a,  Meckel's  cartilage;  E,  epithelial  lamina;  F,  epithelial 
cord;  g,  enamel-organ;  H,  bulb;  I,  follicular  wall;  K,  second- 
ary bourgeon,  from  which  the  enamel-organ  of  the  per- 
manent tooth  originates. 

Fig.  27. — From  lower  jaw  of  a  bovine  embryo,  magnified 
80  diameters. 

a,  (in  the  center  of  the  figure),  Meckel's  cartilage;  b, 
traces  of  ossification;  d,  oral  epithelium;  E,  epithelial  lam- 
ina; F,  epithelial  cord;  g,  enamel-organ;  H,  dental  bulb; 
I,  ''internal  epithelium,"  or  layer  of  ameloblasts;  /',  ex- 
ternal epithelium  of  the  enamel-organ ;  K,  secondary  enamel- 
bourgeon. 


Km..  25. 


%&&MMf& 


Fie.  26. 


d 


Fig.  27. 


F     _ 

K 


198 


SUMMARY. 


Fig.  8.— Ideal  dental  follicle,  before  the  rupture  of  its 
cord.  Drawn  solely  to  show  the  position  of  the  basement 
membrane,  and  the  ^reformative  membranes  of  Raschkow 
and  Huxley.     (For  full  description,  see  p.  89.) 

BM,  basement  membrane;  N,  neck;  S,  sac  or  follicular 
wall;  0,  enamel-organ;  B,  bulb;  E  E,  external  epithelium 
of  the  enamel-organ  and  the  basement  membrane;   E  C 
epithelial    cord;    C  T,   connective    tissue    surrounding  the 
enamel-organ;  E p,  epidermis  or  oral  epithelium. 

The  parts  embraced  between  the  points  where  the  di- 
vergent lines  A  A  terminate  are:  (1)  the  concave  face  of 
the  enamel-organ,  lined  with  a  layer  of  ameloblasts,  or  the 
"internal  epithelium";  (2)  the  membrana  praformativa  of 
Huxley,  or  the  tissue  composed  of  the  basal  coverings  of  the 
ameloblasts;  (3)  the  membrana  prseformativa  of  Raschkow, 
or  the  basement  membrane;  (4)  the  dentine-bulb  itself.— 
(Diagrammatic.)    M.  S.  D.,  del. 

Fig.  28.— Section  through  the  incisive  portion  of  the 
lower  jaw  of  an  ovine  embryo,  measuring  82  millim.  [3% 
inches]  in  length.     (Magnified  260  diam.) 

d,  Oral  epithelium;  c,  lowest  layer  of  cells  in  the  stratum 
Malpighii;  F,  epithelial  cord;  -ST,  bourgeon  of  the  secondary 
cord;  I,  follicular  wall;  H,  dental  bulb.  (See  p.  162-  also 
Fig.  26.) 

Fig.  29.— Vertical  section  of  the  anterior  portion  of  the 
lower  jaw  of  an  equine  foetus,  255  millimetres  [10£  inches] 
in  length,  and  corresponding  to  about  28^  weeks.  (Mag- 
nified 80  diam.) 

a,  Meckel's  cartilage;  b,  traces  of  ossification;  d,  oral 
epithelium;  g,  enamel-organ;  H,  bulb:  /,  layer  of  amelo- 
blasts; K,  bulb  of  the  permanent  tooth,  capped  by  the 
enamel-organ,  with  some  traces  of  the  secondary  cord;  L, 
place  assigned  for  the  development  of  the  cement.  (See 
description,  p.  165.) 


Fio.  88 


A.    A. 


"//?"i/ff,n;r;Mii^::-  ;''%. 


/ 


i  i 
#1 


# 


SI  3 
|Hg H 


// 


Fig.  29. 


A 


■       _.-•■    s&ss^gggS^gggta,         ,,,^"-^:?^^L„ 


L_ia 


iTJ 


g  - 

(_  i 

H 

n  r 

, 

Xj  v-^' 

200  SUMMARY. 

Figs.  30  and  31. — These  cuts  are  taken  from  the  incisive 
region  of  different  human  foetuses,  evidently  not  far  from  the 
sixteenth  week  of  gestation.  A  detailed  description  of  the 
figures  would  be  unnecessary.  The  cuts  are  introduced 
here  simply  because  they  present  one  peculiarity  that  is  not 
represented  in  the  other  figures,  viz,  the  origin  of  the  epi- 
thelial cords  for  the  permanent  incisors  directly  from  the 
epithelial  lamina,  instead  of  their  being  offshoots  from  the 
cords  of  corresponding  temporary  follicles.  These  are  desig- 
nated by  the  letters  E  on  the  right  of  the  figure. 

Though  these  figures  seem  to  establish  the  fact  that  the 
teeth  of  replacement  are  sometimes  derived  directly  from 
the  epithelial  lamina,  yet  we  must  not  regard  these  as  con- 
clusive evidence  until  they  are  fully  verified  by  other  skill- 
ful histologists. 

For  the  drawings  of  these  1  am  indebted  to  my  friend 
Dr.  Black.     (See  description,  p.  137.) 


Fig.  31.    £  KU*, 


202  SUMMARY. 

Fig.  32. — "From  the  upper  jaw  of  a  kitten  about  the 
time  of  birth. 

a,  Oral  epithelium;  b,  bone  of  jaw;  c,  neck  of  enamel- 
organ;  d,  dentine  papilla;  e,  enamel-cells;  /,  stellate  retic- 
ulum; h,  tooth-germ  of  the  permanent  tooth,  the  enamel- 
organ  of  which  is  derived  from  the  neck  of  its  predeces- 
sor."— From  Tomes'  Man.  of  Dent.  Anat. 

Fig.  33. — A  cut  through  the  follicle  of  a  lower  temp, 
molar  of  a  human  foetus,  20  centimetres  [8  inches]  in  length; 
about  the  seventeenth  week  of  gestation.  (Magnified  80 
diam.) 

a,  Meckel's  cartilage;  b,  traces  of  ossification;  c,  c,  dental 
artery  and  nerve;  d,  epithelium  ;  E,  enamel-organ;  F,  cord 
of  the  temporary  follicle;  //,  bulb;  /,  follicular  wall;  K, 
cord  of  the  permanent  follicle.     (See  p.  152.) 

Fig.  34. — Section  of  the  lower  jaw  of  a  human  foetus, 
23%  centimetres  [91  inches]  in  length;  corresponding  to 
about  the  eighteenth  week.    (Magnified  80  diam.) 

K,  Cord  or  bourgeon  of  the  secondary  follicle;  L,  point 
where  its  separation  from  the  primitive  cord  is  being 
effected;  a,  Meckel's  cartilage  diminished  by  absorption; 
b,  bone  of  the  jaw;  c,  (upper)  dental  artery,  (lower)  dental 
nerve;  d,  epithelium;  E,  originally  the  cord  of  the  tem- 
porary follicle,  but  now  the  sole  property  of  the  permanent 
one.     (See  p.  153.) 


1^ 


Fig.  33. 


Fig.  34. 


v^' 


E_f 


H^ 


204  SUMMAKY. 

Fig.  35. —  Section  on  a  line  with  the  follicle  of  the  first 
permanent  molar.  Human  subject,  three  months  after 
birth.     (Magnified  80  diam.) 

b,  Maxillary  bone;  c,  c,  dental  artery  and  nerve;  E,  cord 
of  the  follicle  of  the  first  permanent  molar;  g,  enamel- 
organ;  H,  bulb  of  the  first  permanent  molar;  K,  bourgeon 
of  the  enamel-organ  of  the  second  permanent  molar.  (See 
p.  156.) 

Fig.  36. — Vertical  section  of  the  lower  jaw  of  a  human 
foetus,  measuring  47  centimetres  [18%  inches];  correspond- 
ing to  nearly  the  thirty-ninth  week  of  gestation.  The  figure 
represents  a  cut  passing  through  the  follicle  of  a  bicuspid. 

b,  Bone  of  the  jaw;  d,  oral  epithelium;  g,  enamel-organ; 
H,  dental  bulb;  K,  debris  of  the  cord  of  a  permanent  fol- 
licle; K'  K',  epidermal  globules.  Follicle  for  the  perma- 
nent tooth  connected  with  the  debris  of  its  cord,  K. 

Fig.  37. — Vertical  transverse  section  through  the  incisive 
region  of  the  lower  jaw  of  a  human  foetus,  measuring  38 
centimetres  [15i  inches].     (Magnified  80  diam.) 

b,  Bony  formation ;  d,  oral  epithelium;  g,  enamel-organ; 
H,  dental  bulb;  J,  cord  of  the  permanent  follicle;  K,  debris 
on  the  follicular  wall  of  the  primitive  follicle  and  from  its 
cord;  K',  epithelial  globule;  L,  enamel-organ  of  the  per- 
manent tooth. 


K' 
■K* 


Fig.  37. 


fll 


206  SUMMARY. 

Fig.  38. — From  the  lower  jaw  of  an  ovine  embryo,  mag- 
nified 80  diameters;  showing  the  completed  dental  follicle 
and  the  sun-ounding  tissues. 

a,  Meckel's  cartilage;  b,  traces  of  ossification;  c,  lowest 
layer  of  the  epithelial  cells;  d,  oral  epithelium;  F,  amelo- 
blastic layer;  F,  (lower)  external  layer  of  the  enamel-organ — 
a  continuation  of  the  layer  of  ameloblasts;  g,  stellate  retic- 
ulum of  the  enamel-organ;  H,  bulb;  7,  follicular  wall;  K, 
buddings  from  the  cord. 

Fig.  39. —  From  a  human  embryo,  20  centimetres  [8 
inches]  in  length.     (Magnified  80  diain. ) 

a,  Meckel's  cartilage;  b,  bone;  c,  c,  artery  and  nerve; 
d,  oral  epithelium;  E,  cord  of  the  first  permanent  molar 
originating  from  the  lamina;  F,  debris  of  the  cord  of  the 
preceding  follicle;  g,  muscular  insertions.  (See  description, 
p.  155). 

Fig.  40. — A  section  of  the  skin  of  a  human  foetus,  20 
centimetres  [8  inches];  about  the  seventeenth  week  of 
gestation;  showing  the  complete  analogy  in  the  develop- 
ment of  the  hair  and  the  teeth. 

.«,  Filous  follicle  quite  well  developed,  with  its  bulb 
forcing  back  the  epithelial  cells  and  forming  a  cap  for  itself; 
b,  simple  epithelial  bourgeon;  c,  epithelial  bourgeon,  with 
the  bulb  just  appearing. 


?%&& 


" 


. 


m  . 


. . 


208  SUMMARY. 

Fig.  41. —  Section  taken  from  the  jaw  of  an  embryonal 
calf,  after  the  rupture  of  the  epithelial  cord.  (Magnified 
260  diam.) 

This  cut  embraces  the  region  external  to  the  follicle  (a), 
which  latter  is  not  represented  in  this  figure,  b,  Epithelial 
buddings  upon  the  follicular  wall;  c,  epithelial  lamina,  still 
entire;  E,  E,  buddings  from  the  epithelial  cord;  F,  globular 
epithelial  mass  in  the  lamina. 

Fig.  42. —  Section  taken  from  a  bovine  embryo,  and  em- 
bracing the  same  territory  represented  in  Fig.  41. 

a,  Segment  of  the  follicular  wall;  b,  epithelial  buddings 
upon  the  wall;  c,  prismatic  layer  of  the  oral  epithelium; 
d,  oral  epithelium;  E,E,  debris  and  buddings  of  the  cord; 
F,  epithelial  globules  from  the  debris  of  the  epithelial 
lamina.     (Magnified  100  diameters.) 

For  the  physiological  importance  attributed  to  these 
epithelial  proliferations,  see  pp.  66  and  179. 


Fig.  41. 


Pig.  12. 


^um 


■  "  \ 


^x\i 


(ag/a>»2gv 


fe*A 


Sit 


210  SUMMARY. 

Fig.  43. — Vertical  transverse  section  of  the  lower  jaw  of 
a  human  foetus,  56  centimetres  [22f  inches]  in  length; 
corresponding  to  about  the  period  of  birth.  (Magnified  80 
diam.) 

b,  Osseous  formation;  d,  oral  epithelium;  E,  lowest  layer 
of  the  Malpighian  stratum;  F,  debris  of  the  epithelial 
lamina;  g,  enamel-organ;  H,  dental  bulb;  I,  follicular 
wall;  j,  cap  of  dentine  and  enamel;  K,  debris  of  the  second- 
ary cord;  L,  bulb  of  the  permanent  tooth,  capped  with  the 
enamel-organ. 

Fig.  44. —  Dental  follicle  of  a  permanent  tooth  of  a  cat; 
vertical  and  transverse  section.  From  a  preparation  of 
Thiersch.  (Magnified  14  diam.)  Taken  from  the  fifth  edi- 
tion of  Kolliker's  Elements  of  Human  Histology. 

A,  Dental  bulb,  the  external  zone  of  which  is  formed  by 
the  odontoblasts;  b,  dentine;  c,  enamel;  d,  "internal  epithe- 
lial layer  of  the  adamantine  organ  or  adamantine  mem- 
brane" [the  layer  of  prismatic  or  columnar  cells  that  we 
denominate  ameloblasts];  e,  gelatinous  tissue  of  the  en- 
amel-organ [stellate  reticulum];  /,  external  epithelial  layer 
of  the  adamantine  organ  [enamel -organ];  g,  internal  layer 
of  the  dental  sac  or  follicular  wall;  h,  external  layer  of  the 
same. 

[The  white  space  seen  between  the  layer  of  ameloblasts 
and  the  developing  enamel  is  evidently  accidental.  See 
remarks  on  Fig.  24.] 


t^'iv  £v»'tv 

e — £  |$K 


I;A> 


K 


INDEX 


Adamantine  membrane,  22,  109 
Aggregations  of  epithelium,  125 
Amelification,  91 
Ameloblasts,  83,  91,  109,  151,  153 
Amorphous  layer,  17,  101 
Apophyses,  28 

Atrophy  of  Meckel's  Cartilage,  37 
Authors'  introduction,  47 
Bar  of  the  solipeds,  diastema,  55 
Basement  membrane,  14,  17,  21,  24,  88  and  89 
Bourgeons,  28,  44,  122,  130 
primitive,  135 
secondary,  134,  136 
Bourrelet,  epithelial  band,  54 
Cartilago  dentalis,  54 
Cell,  apology  for  use  of  the  term,  44 
Cells,  epidermal,  25 

epithelial,  in  different  stages  of  development,  20 
aculeated,  imbricated,  prickle,  spinous,  ridged,  20 
columnar,  21,  23 
cylindrical,  21 
polygonous,  22,  116,  132 
prismatic,  21,  81,  83 
Cement,  coronal,  111 
Cemental  organ.  111 
Chronology  of  the  dental  follicle,  periods  of  appearance  of 

its  parts,  147 
Chronological  table  of  dental  follicle,  160 
Corium,  12,  14 
Cord  of  temporary  teeth,  128 

permanent  teeth,  128 
Corneous  stratum,  15,  17,  19,  20,  23 
Corneous  leaf  or  plate,  of  Remak,  18 
Cortical  layer  of  enamel-organ,  82 
Cuticle,  17 
Cutis  vera,  14 

Definition  of  foetus,  embryo,  follicle  and  bourgeon,  41 
Dental  follicle,  89,  105,  111 

its  genesis  and  formation,  theories  of  criticised,  169 


INM-.X. 


213 


Dental  follicle,  definition  of,  42 

origin  and  formation  of,  4!) 
Dental  germ,  107 

groove.  135.  150     • 
sacs,  LOT 
sacculus,  42,  '.'s 
Dentine-bulb,  25,  42,75,90,100,  L12 

origin  and  growth  of,  98 
I)entine-cap.  152 
Dentinal  papilla,  25,  42,  75.  96 
Dentinal  sheet  of  tissue,  66 
Dermal  stratum,  21 
tissues,  16 
Dermis  (derm  or  dermal,  12,  14.  16,  24.  2G 
Diagram  of  mucous  membrane.  13 
Diastema,  or  bar.  55 

Diverticulum,  132  '  . 

Double  pellucid  layer,  between  ameloblasts  and  tissues  ot 

pulp.  H8 
Early  development  of  the  jaws,  27 

Ecderon  and  enderon,  14    _  _  .     ,   1Aft 

Embryos,  canine,  ovine,  bovine  and  equine,  studyot,  lbi  to  iw 
Kmbryoplastic  elements  of  incipient  dental-bulb,  95,  1WJ 
Enamel,  formation  of,  due  to  internal  epithelium.  82,  »6 
Enamel-cells,  ameloblasts,  83 

-membrane,  22 
Enamel-organ,  21,  42,  83.  90,  93,  96,  151 
its  development,  65 
as  fully  developed,  75 
as  part  of  the  dental  follicle,  107 
of  the  permanent  tooth.  142 
Enamel-organs  of  supernumerary  t<  eth,  66 
Epiblast,  18,  25 
Epidermal  cells.  25 

membrane,  Is 
stratum.  21 
Epidermis,  11,  14.  1!).  114.  119 
Epithelial  band,  description  of.  54.  58,  62,  14!) 

Kiilliker's  discovery  of,  175.  176 
Epithelial  cord,  66.  150 

as  determining  the  place  and  form  of  tooth.  .». 
when  its  course  is  finished,  123 
of  permanent  follicles,  point_ of  origin,  13 1,  138 
in  embryo  of  two  months,  150 
Epithelial  lamina,  its  origin  and  development,  62 

at    the  period  the  enamel-organ    loses  connection 
with  it.  105 


214  INDEX. 


Epithelial  lamina,  phenomena  located  in  it  after  rupture  of 
cord,  115 

sometimes  the  place  of  origin  of  cords  of  anterior 
permanent  teeth,  13? 

place  of  origin  of  the  cord  of  first  permanent  mo- 
lar, 143,  144 

proliferations,  phenomena  of,  121,  122 
Epithelial  ridg'e  or  band,  its  origin,  etc.,  51 
Epithelium,  11,  13,  18,  112 

pavimentous  or  tessellated,  20 
Errors  of  early  observations,  cause  of,  175 
External  germinal  layer,  or  epiblast,  18 

osseous  arch,  35 
First  permanent  molar,  its  place  of  origin,  144 
Follicle,  definition  of,  43 

epithelial  proliferations  upon,  121 
Follicular  wall,  42,  108 

network  of  vessels  upon,  112 

buddings  upon,  120,  122 

not  closed  at  twelfth  week,  152 
Formation  of  enamel,  due  to  internal  epithelium,  82,  83 
Formed  material,  Beale,  22,  23 
Fusiform  bodies,  composing  incipient  dental  bulb,  95 
Genesis  and  growth  of  the  dental  follicle,  theories  of  criti- 
cised, 169 

of  follicle,  true  order  of,  174 

of  follicle, etc.,  summary  of  facts  concerning,  180, 181 

of  follicle,  conclusions  regarding,  181  to  184 
Glandula?  tartaricse,  124 
Hare-lip,  its  origin,  31 
Horny  layer  of  the  epidermis,  23 
Human  embryo,  relation  between  size  and  age,  148 
Incisive  or  intermaxillary  bourgeons,  origin  of,  etc.,  29,  31 

period  of  union  with  the  maxillary  bourgeons,  50 
Incisive  region,  40 
Initial  spheroid,  of  Guillot,  173 
Intermaxillary  bones,  30,  38 

processes,  31 

suture,  39 
Intermediate  membrane,  of  Henle,  12,  18 
Internal  cartilaginous  arch,  35 

epithelium  of  the  enamel-organ  of  Kolliker,  22 
Introduction,  authors',  47 

Lamina,  epithelial,  62,  70,  105,  115,  137,  144 
Laminated  membrane  of  follicular  wall,  106 
Last  molar,  its  origin,  144 


INDEX.  -I' 


Lateral  buddings  of  primitive  cord,  •  •-' 
Malleus,  termination  of  Meckel's  cartilage,  33 

ossification  of  its  cartilage  .  :'>i 
Malpighian  stratum,  15,  17.  30,  84 
Manimillated  form  of  mcipienl  dental  bulb,  ■'•> 
Mandibular  processes,  82 
Maxillary  bourgeons,  union  with  intermaxillary,  ■>" 

rampart,  52 
Meckel's  cartilage,  27,  32,  50,  149 
Membrana  adamantina,  of  Raechkow,  22 

Eboris,  91 

praVurmativa  of  Rasehkow.  18.  88,  90.  101,  10(5 
prsformativa  of  Huxley,  88,  90 
propria,  12 
Mesoblast,  the  origin  of  the  dermis,  19 
period  at  which  developed,  25 
Mucosa,  1-4 
Mucous  layer,  12 
Mucous  membrane,  9 

Odontol .lasts,  tissue  in  which  they  first  appear.  101 
Odonto>n.nir  parj,  or  the  generating  part  of  the  teeth,  ol 
Odontomes,  159  . 

Oral  epidermis,  divisible  into  two  lamina1,  19 
Origin  and  formation  of  the  dental  follicle,  49 
Origin  and  formation  of  the  dental  bulb  and  follicular  wall, 

93 
Pars  papillaris,  or  i  r>   j-  .->- 
Papillary  layer.       f      '       '  10    ,-    .,- 

Pars  reticularis,  reticulary  layer.  Id,  lo.  &a 
Pellucid  layer.  v^ 
Periplast  ol  Huxley.  22 

Permanent  follicles  that  Lave  been  preceded  by  temporary 
ones,  129 
commencement  of,  153 
Phenomena  that  follow  formation  of  follicle,  etc.,  115 
Plateau  of  the  prismatic  cells.  s7 
Premaxillse,  40 

Primitive  bourgeon  of  the  follicle,  65 
Primitive  papilla.  95 
Primitive  follicle  after  rupture  of  cord.  123 

modifications  in  surrounding  parts.  185 
in  relation  to  origin  of  secondary  cord,  188 
Primitive  cord,  prolongations  of,  128 

point  from  which  secondary  bourgeon  starts,  140 
Prismatic  layer  of  cells,  28,  59,  82,  109 
Processes,  apophyses  or  bourgeons,  28 


2 1  6  INDEX. 

"  Proper"  mucous  membrane,  13,  14 

Pulp  of  enamel- organ,  stellate  arrangement  of,  80 

Raschkow's  theory  of  origin  of  follicle,  171 

Reticulary  layer,  13,  15,  25 

Ruptured  cord,  135 

Scarf-skin,  17 

Second  molar,  origin  of,  144 

Secondary  bourgeon,  its  descent  into  dental  groove,  134 

in  lower  animals,  136 

and  point  of  origin,  direction  it  takes,  140 
Secondary  cord,  139 

development  of,  153 

separation  of,  154,  155 
Secondary  follicle,  123,  141 
Semilunar  area,  origin  of  dentine  germs,  98 
Skin,  analogous  to  mucous  membrane,  16 
Stellate  bodies,  transformation  of  cells  of  the  enamel-organ, 

69,  77 
Stratum  corneum,  23 

Malpighii,  12,  20 

Malpighii  prismatic  layer  derived  from,  59 

intermedium,  84,  153 
Subcutanea,  15 
Subdermal  areolar  tissue,  25 
Subdermis,  15 
Submucous  tissue,  25 
Submucosa,  13,  15 
Superior  maxillary  processes,  31 
Tartaric  glands,  124 
Tela  mucosa,  13,  15 

Temporary  follicles,  generally  the  source  of  the  twenty  an- 
terior permanent  teeth,  137 
The  epithelial  lamina  and  genesis  of  enamel-organ,  62 
The  mode  of  origin  of  follicles  of  permanent  teeth,  127 
Third  molar,  place  of  origin,  138, 145 
Tongue,  apophyses,  etc.,  28 
Translator's  introduction,  9 
True  epidermis,  17 

Tubercles,  bourgeons,  processes,  etc.,  28 
Upper  jaw,  its  development,  50 
Vessels  of  the  bulb,  126 
Visceral  arch,  28 
Wisdom  tooth,  its  origin,  138,  144 


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RK880 

Legros 


L52 
Copy  1 


Origin  and  formation  of  the  dental 
follicle. 


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